Dai Cuong Hc Th Cuong

7/25/2019 Dai Cuong Hc Th Cuong

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LI NI U

Cun sch i cng ha hu c c bin son theo ni dung ca chngtrnh o to h chnh quy mn hc ny bc i hc v cao ng oc ging

dy trong nhiu nm trng i hc S phm i hc Nng.

Ni dung cun sch gm c 6 chng: M u; Cu trc khng gian phn

t hp cht hu c; Lin kt trong ha hc hu c; Hiu ng cu trc phn t hp

cht hu c; Cc axit baz hu c; Phn ng hu c. Sau mi chng c mt s

cu hi, bi tp cho sinh vin t gii nhm cng c thm cc kin thc v l

thuyt.Cun sch l ti liu hc tp cho sinh vin cc chuyn ngnh ha hc s

phm, ha dc, ha sinh mi trng; lm ti liu tham kho cho cn b lm

cng tc ging dy, nghin cu khoa hc, cho cc hc vin cao hc, nghin cu

sinh cc chuyn ngnh ha hc.

Trong qu trnh bin son chc chn cn nhiu thiu st cha tht lm hi

lng bn c; Chng ti rt mong nhn c nhng kin ng gp hon thin

hn.

Tc gi


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CHNG 1: M U

1.1. i tng ca ho hc hu cHo hc hu c l mn khoa hc nghin cu thnh phn v tnh cht cc

hp cht ca cacbon.Trong thnh phn ca cc hp cht hu c, ngoi cacbon cncha nhiu nguyn t khc nh: H, O, N, S, P, halogen Nhng cacbon c coil nguyn t c bn cu to nn cc hp cht hu c.

Ho hc hu c nhanh chng tr thnh mt ngnh khoa hc ring v ccnguyn nhn di y:

- S lng cc hp cht hu c tng ln nhanh chng v t ti con skhng l khong trn 5 triu cht, trong c nhng cht ng vai tr v cngquan trng i vi s sng nh protein, axit nucleoic, hocmon

- Nguyn nhn dn n s tn ti mt s lng rt ln cc hp cht hu cl ch cc nguyn t cacbon c kh nng c bit l va c th lin kt vi ccnguyn t ca cc nguyn t khc v va c th lin kt vi nhau thnh mchcacbon cc kiu khc nhau. Do , cc hp cht hu c xut hin cc hin tngng ng, ng phn, h bin v nhng biu hin phong ph v ho lp th.

- Cc lin kt ch yu trong ho hu c l lin kt cng ho tr nn c tnhcht l hc v ho hc khc cc hp cht v c. Cc hp cht hu c mn cm vinhit hn, khng bn nhit cao, a s chy c, t tan trong nc, s tanc thng t hoc khng phn li thnh ion. Cc phn ng thng chm, thunnghch v theo nhiu hng.

1.2. S lc lch s pht trin ca ho hc hu cT thi xa xa, ngi ta bit iu ch v s dng mt s cht hu c

trong i sng nh gim, mt s cht mu hu c, ru etylic, Thi k gi kimthut, cc nh ho hc bit iu ch mt s cht hu c nh ete etylic, ur

Vo khong cui th k XVIII, u th k XIX, cc nh ho hc chittch c t ng thc vt nhiu axit hu c nh axit oxalic, axit xitric, axitlactic v mt s baz hu c. Nm 1806, ln u tin Berzelius dng danh tho hc hu c ch ngnh ho hc nghin cu cc hp cht c ngun gc ngthc vt. Thi im ny c th xem l im mc nh du s ra i ca mn hohc hu c.

Nm 1815, Berzelius a ra thuyt lc sng, mt lun thuyt duy tm,cho rng cc hp cht hu c ch c th to ra trong c th ng, thc vt nh mtlc sng c bit m bn tay con ngi khng th iu ch c trong cc bnh,l, ng nghim nh i vi cc cht v c. Thuyt lc sng thng tr ho hchu c trong nhiu nm. Sau thuyt ny dn dn b nh nh cc cng trnhtng hp cc cht hu c t cc cht v c. Nm 1824, Wohler tng hp caxit oxalic, mt axit hu c in hnh (bng cch thu phn dixian l mt cht v


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c). Nm 1828, cng chnh Wohler tng hp c ure (vn c trong nc tiung vt) t amoni xyanat, cng l mt cht v c:

NH4CNO H2N CO NH2

Chnh pht minh ny lm sp bc tng ngn cch trc gia hohc v c v ho hc hu c, lm cho cc nh ha hc tin rng c th t tng hpc cc cht hu c trong phng th nghim m khng cn c s tham gia camt lc sng no c. Tip theo , Bectl tng hp c cht bo nm 1854v Bulerp tng hp c ng glucoza t formalin nm 1861. Cho n nay,hng triu cht hu c c tng hp trong cc phng th nghim v trong cngnghip. Khng nhng con ngi bt chc c thin nhin trong nhiu lnh

vc m con ngi cn sng to ra c nhiu vt liu hu c, nhiu cht hu ccc k quan trng, qu gi khng c trong t nhin.Tuy nhin, tn gi hp cht hu c vn c duy tr, nhng khng phi

vi ngha nh trc y l cc cht c ngun gc ng, thc vt m n mangmt ni dung mi, l cc hp cht ca cacbon.

1.3. Nhng quan im v cu to ca hp cht hu cCu to ca hp cht hu c l s phn b ca cc nguyn t hoc nhm

nguyn t trong khng gian ca mt phn t.

1.3.1. Thuyt gc (Radial, k hiu R)Thuyt cu to ho hc ca cc hp cht hu c c pht trin mnh

u th k XIX. T nhng cng trnh ho hc ca Lavoisier, Berzelius, Wohler,Liebig cho thy trong nhng phn ng hu c c nhng phn cht c cu trckhng thay i chuyn t cht u sang cht cui gi l gc. Quan nim ny cho ra i thuyt cu to ho hc u tin l thuyt gc. Thuyt gc cho rng:

phn t hu c gm 2 phn:- Gc l phn khng bin i trong cc qu trnh chuyn ha ha hcV d: Gc axetyl: CH3CO-

Gc benzoyl: C6H5CO-- Phn kt hp vi gc l cc nguyn t hay nhm nguyn t khc nhauu im: Phn loi c mt s cc hp cht ha hc hu c theo gc cu

to, t c th d on c tnh cht ca cc nhm hu c.Nhc im: Ch phn bit c nhng hp cht n gin, khng c

ngha i vi cc hp cht phc tp do phm vi ng dng b.

1.3.2.Thuyt kiuThuyt kiu ca Dumas ra i chia ra lm hai dng:


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- Dng ho hc: gm nhng cht c tnh cht ho hc ging nhau nh axitaxetic v axit cloaxetic.

- Dng c hc: gm nhng cht c cng s nguyn t nh nhau nhng tnhcht khc nhau nh axit axetic v ru etylic.Theo thuyt kiu ny, ngi ta thit lp c nhiu kiu hp cht

hu c nh:

- Kiu nc ca Williamson:

- Kiu amin ca Wurtz v Hofmanm:

H

H

H

N

- Kiu clorua hiro ca Gerhardt:

H

Cl

CH3

Cl

C2H5

Cl

C2H3O

Clhyrcloruam tylclorua tylclorua ax tylclorua

Trong quan trng nht l kiu metan ca Kkul:

H

H

HH

C

Ngi ta xc nh c rng, cc hp cht hu c c c trng bngnhng phn ng kiu xc nh.

u im:+ Thuyt kiu c ng gp to ln vo vic phn loi cc hp cht hu

c, thun li cho vic tm kim.

H

HO

CH3

HO

CH3O

CH3


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+ Nghin cu nhng phn khng thay i trong cc chuyn ho ho hc vcng gii thch c phn no s thay i .

Nhc im:+ Do s kiu nhiu nn rt phc tp trong vn phn loi, hn ch trongvic s dng.

+ C nhng hp cht hu c khng th sp xp theo mt kiu no c.

1.3.3. Thuyt ButleropNi dung ca thuyt cu to ho hc ca Butlerop bao gm cc lun im:- Tt c cc nguyn t trong hp cht hu c kt hp vi nhau theo mt trt

t xc nh. Trong vic kt hp , cc nguyn t tiu ph mt phn i lc hohc ca mnh. Trt t kt hp ca cc nguyn t v c tnh ca cc lin kt trong

phn t l cu to ho hc.- Nguyn t ca cc nguyn t to nn phn t lin kt vi nhau theo ng

ho tr ca mnh. Trong phn t cht hu c, cacbon bao gi cng c ho tr 4.Cc nguyn t cacbon chng nhng c th lin kt vi cc nguyn t ca ccnguyn t khc m cn c th lin kt vi nhau thnh mch.

- Tnh cht ca cc cht khng ch ph thuc vo thnh phn v s lngnguyn t ca cc nguyn t m cn ph thuc vo cu to ho hc ca hp cht.

- Cu to ho hc ca cc cht c th xc nh c khi nghin cu tnhcht ca chng. Cu to ho hc ca mi cht c th biu din bng mt cng thcxc nh l cng thc cu to. Cng thc cu to va phn nh cu to ho hcca phn t va th hin nhng tnh cht c bn ca hp cht.

- Tnh cht ho hc ca mi nguyn t v nhm nguyn t trong phn tkhng phi l bt bin m thay i tu thuc vo cc nguyn t v nhm nguynt lin kt trc tip vi nhau mnh hn nh hng gin tip.

Th thch qua thi gian, thuyt cu to ho hc t ra ng n v su sc.T nhng lun im s gin y, ngy nay pht trin thnh nhng thuyt hini v cu to v lin kt, v hiu ng, v ho hc lp th,

1.4. Cch biu din cng thc cu to hp cht hu c

Cng thc cu to phng biu din cu trc ca phn t quy c trn mtmt phng, thng l mt phng giy.

1.4.1. Cng thc LewisCng thc Lewis biu din cc lin kt gia cc phn t hay s electron

ho tr ca mi nguyn t bng s electron. S electron l bng tng electron cacc nguyn t ng gp vo v cc nguyn t c xu hng to trng thi electronln nht c th c c vng electron bn vng ca kh tr.V d:


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O C O C

H

HH

H

C C

H

H

H

H

Cc cng thc c th mang in tch, thng gi l in tch hnh thc hayquy c:

N+H

H

H

H

Ion amoni

CH

O

H

H

Ion metoxit

Khi nhng tiu phn khng c vng bt t th thng l nhng tiuphn trung gian khng bn, c kh nng phn ng cao v trong phn ng c xuhng nhanh to thnh cu trc electron bt t.

H

HH C+

Cation metyl

H

HH C

u im:D k hiu, cho thy c bn cht ca qu trnh phn tch.Nhc im:Phc tp cho qu trnh biu din, d gy sai st. Trong mt s

trng hp khng biu din c.

1.4.2. Cng thc Kekule n gin trong cch biu din ca Lewis, ngi ta quy c biu din

cc lin kt trong phn t bng vch ngang thay cho cp electron lin kt.V d:

N HH

H

H

C

H

H O

H

C HH

H

C HH

H

Trong cc hp cht c mang in tch cng c th thay th kin kt bngmi tn t cht cho ti cht nhn:

Gc metyl


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H O N

O

O H O N

O

OHay

n gin trong cch biu din cng thc, c th n cc gch lin kt, n

mt phn hay ton phn tu thuc vo yu cu cch biu din, ng thi cng bqua cc cp electron khng lin kt, gi l cng thc rt gn:

CH3CH2CH3, CH3 CH2 CH3, CH3CH2CH2 H

Ngoi ra, mt cht c th biu din di nhiu dng cng thc, chng hn:

CH3 CH2 CH3 CH3 CH2

CH3

CH2

CH3

CH3

u im:Khc phc nhc im ca cng thc Lewis, n gin v phnnh tht bn cht ca lin kt.

Nhc im:Khng thy s gp chung electron. Trong trng hp phnct d ly th khng thy c hin tng.

Ch : Trong mt s trng hp c bit cc hp cht hu c mch vng,ngi ta thng khng biu din k hiu ca cc nguyn t cacbon v hidro.

1.5. Danh php hp cht hu cC 4 loi danh php ch yu:

1.5.1. Danh php thng thngL tn c gi theo ngun gc thu nhn c cht , theo tn ca ngi

tm ra n hay mun ca ngi tm ra n, theo phng php thu nhn c cht

.

V d: Axit fomic: HCOOH (Fomica: Kin)Axit axetic: CH3COOH (Acetus: Gim)Mentol: C10H20O (Mentha piperita: Bc h)

1.5.2. Danh php hp lLy tn ca mt hp cht hu c lm tn gi u sau gi tn ca cc hp

cht hu c khc tng t theo tn ca cc cht hu c u.


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V d:

C OH

H

H

H

Cacbinol

C OH

H

H

CH3

Metyl Cacbinol

C OH

H

C6H5

CH3

Metyl Phenyl Cacbinol Nhc im: i vi cc hp cht phc tp th khng th gi tn c.

1.5.3. Danh php thng miL tn ca cc hp cht ho hc hu c c s dng trn th trng do cc

hng sn xut t tn.V d: Cc loi thuc nhm: Rongalit C (NaHSO2.CH2O.2H2O): dng in hoa

Rongal P ( Dn xut ca axit sunfonic): dng nhum huyn ph.

1.5.4. Danh php IUPAC (Hip hi ho hc quc t: International Union PineAnd Applycation Chemistry)

1.5.4.1. Tn gc - chc

V d:

CH3CH2 Cl CH3CH2 O COCH3 CH3CH2 O CH3Etyl clorua Etyl axetat Etyl metyl ete

1.5.4.2. Tn thay thTn khng y :

V d:H3C CH3 H3C CH2Cl H2C = CH2

Etan Cloetan Etan

* Tn nhm th:

TN PHN GC TN PHN NH CHC

TN PHN TH TN MCH CACBON CHNH TN PHN NH CHC(c th khng c) (bt buc phi c) (bt buc phi c)


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Cc nguyn t ca cc nguyn t th gi tn theo tng nguyn t

OH : Hiroxyl

OR : AncoxylCH3O : Metoxyl

C6H5O : PhenolxylCH3CO : Axetyl

C6H5 : Phenyl

C6H5CH2 : BenzylNO2 : Nitro

NH2 : Anmino

CN : Nitryl

SH : MecaptanSO3H : Sunfonic

R - : Ankyl

- Chn mch chnh: Chn mch cacbon di nht cha cc nguyn t cacbonlin kt cacbon lm mch chnh. Chn mt nhm chc c u tin nht lmnhm chc chnh, cc chc cn li l phn th.

u tin nhm chc:

-COOH > -COO- > -CHO > -CO- >-OH >-NH2> -O-

- nh s th t:Ta nh s th t t bn phi sang bn tri hoc tri qua sao cho tng cc

ch s ca cc nhm th l nh nht. Trng hp khi nh s t u ny n ukia m thu c mt s dy ch s ca cc nhm mch nhnh khc nhau th phisp xp chng li theo th t tng dn. Dy c tng cc ch s nh nht c xeml dy c ch s u nh nht.

V d:

* Tn phn nh chc:An, en, in, ol, al, on, oicTn y : Cu hnh + du quang hot + tn gi khng y

gi tn hp cht hu c, cn thuc tn cc s m v tn mch cacbonnh sau:

CH3 CH2 CH CH2 CH3

CH33-metylpentan

CH3 CH CH CH2 CH3

CH32-metylpentan

2


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S M MCH CACBON CHNH

1: mono C met2: i C C et

3: tri C C C prop

4: tetra C C C C but

5: penta C C C C C pent

6: hexa C C C C C C hex

7: hepta C C C C C C C hep

8: octa C C C C C C C C oct

9: nona C C C C C C C C C non10: deca C C C C C C C C C C dek

1.6. Phn loi cc hp cht hu cHp cht hu c c phn thnh hidrocacbon v dn xut ca

hidrocacbon.- Hidrocacbon l nhng hp cht c to thnh t hai nguyn t C v H.Gm 3 loi:+ Hidrocabon no (Ankan): CH4, C2H6

+ Hidrocacbon khng no gm anken: C2H4v ankin: C2H2+ Hidrocacbon thm (Aren): C6H6- Dn xut ca hidrocacbon l nhng hp cht m trong phn t ngoi C, H

ra cn c mt hay nhiu nguyn t ca cc nguyn t khc nh O, N, S,halogenbao gm: dn xut halogen nh CH3Cl, ancol nh: CH3OH, axit nh:CH3COOH,


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CU HI V BI TP

Bi 1. Hynunhng quan im v cu to ca hp cht hu c?Bi 2. Hy trnh by cc cch biu din cng thc cu to hp cht hu c?Bi 3.Gi tn thay th cc hirocacbon sau theo danh php IUPAC:

CH3 CH2 CH2 C CH2CH2 CH3

(C) (D)C C CHCH3 CH2 CH CH2CH CH2

Bi 4.Gi tn thay th cc hirocacbon sau theo danh php IUPAC:

CH3

CH2 CH3

CH3

(E)(F)

Bi 5.Gi tn thay th cc HCHC sau theo danh php IUPAC:

NH2 CH2 CH2 CH2OH OH

CH3 CH

Cl

CH3 CH3 CH CH C CH2CH3 CH3NO2(X) (Y) (Z) (T)

Bi 6. Gi tn thay th cc HCHC sau theo danh php IUPAC:

CH3 CH CH

OH CH3

CH C

Cl

C CH3O

CH2NH2

CH C C C OH

OCH3 Bi 7.Vit CTCT ca cc hp cht hu c sau:a. 5-etyl-3-metylhept-3-en-1-in b. 2-metylxiclopenta-1,3-ienc. 4-brombut-3-enal d. 3-clo-2,4-imetylpentan-1-olBi 8.Vit CTCT ca hp cht cacbonyl cha vng benzen c CTPT C8H8O?Bi 9. Hy phn loi hp cht hu c?


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TI LIU THAM KHO

1. Phan Tng Sn, Trn Quc Sn, ng Nh Ti, C s l thuyt ho hu c,tp 1,2, NXB i hc v trung hc chuyn nghip H Ni, 1980

2. Trn Quc Sn, ng Vn Liu Gio trnh c s ha hc hu c, Tp 1, 2,NXB i hc s phm, 2007.

3. Thi Don Tnh, C s ho hc hu c, Tp 1, 2, NXB Khoa hc v K thut,H Ni, 2006.

4. Thi Don Tnh, C ch v phn ng ha hc hu c (tp 1,2,3),NXB Khoahc v k thut, H Ni, 2008.

5. ng Nh Ti, C s l thuyt ha lp th, NXB Gio dc, H Ni, 1998.6. Hong Trng Ym, Ho hc hu c, NXB Khoa hc & K thut, H Ni,

2002.


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CHNG 2: CU TRC KHNG GIAN PHN T HP CHT HU C

2.1. Chit tch v tinh ch hp cht hu cCc hp cht hu c khi mi iu ch c hoc tch t ng thc vt,thng dng hn hp khng tinh khit. V vy mun nghin cu chng, mun

phn tch nh tnh hay nh lng chng th nhim v trc tin l phi tchchng thnh tng cht ring bit, dng tng i nguyn cht.

2.1.1. Tinh ch cht rn

2.1.1.1. Phng php kt tinha. Khi nimKt tinh l mt qu trnh bin i pha ca mt cht t rn sang lng khi ho

tan cht rn trong mt dung dch bo ho, sau lm lnh dung dch bo ho thu c cht rn kt tinh

b. C s l thuytPhng php kt tinh c dng tch v tinh ch cc cht hu c rn,

da trn nguyn tc l cc cht khc nhau c ho tan khc nhau trong cng mtdung mi. Dung mi thch hp c la chn thng l dung mi trong hotan ca cht cn tinh ch tng kh nhanh theo nhit , tan km nhit thng;khng tan trong tp cht, khng c lc tng tc v mt ho hc i vi cht kt

tinh v sau khi kt tinh li phi d bay hi. Dung mi la phi d kim, r tin.Bng cch to dung dch bo ho nhit cao (thng l nhit si cadung mi), sau ngui dung dch thu c, cht cn tinh ch s lng xungy bnh (hay y cc), cc tp cht s li trong dung dch. Bng cch kt tinhli mt s ln trong cng mt dung mi, hoc trong cc dung mi khc nhau,ngi ta c th thu c tinh th cht cn tinh ch dng kh tinh khit. Cng ckhi ngi ta dng mt dung mi c ho tan vi tp cht nhiu hn loi tpcht khi cht rn cn tinh ch. Dung mi thng dng l nc, alcol etylic, ancolmetylic hay mt alcol thch hp khc, axeton, axit axetic, ete, benzen, cloroform,etyl axetat....hoc i khi hn hp gia chng.

Khi cn tch hai hay nhiu cht c cha trong hn hp vi nhng lngtng ng nhau, ngi ta dng phng php kt tinh phn on. Cht kt tinhli c ht u v trng. Khi c cht rn kt tinh, ta cn xc nh nhit nngchy ca n bng ng mao qun gn vi nhit k nhng trong mt dung mi cnhi si cao, hoc cch khng kh, hoc nh mt my chuyn dng ri ichiu vi hng s vt l ca cht cho, bit c cht tinh khit hon toncha.

2.1.1.2. Phng php thng hoaa. Khi nim


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Thng hoa l mt qu trnh bin i pha ca mt cht t trng thi rn sangtrng thi hi m khng thng qua trng thi lng.

b. C s l thuytMt s cht nh it, long no, naphtalen, menton, clorua st (III),... c khnng thng hoa, v vy ngi ta c th dng phng php thng hoa p sutthng hoc p sut thp tinh ch chng.

Phng php tin hnh: Gia nhit mt cht rn bay hi, lm lnh hi cacht rn th ta s thu c cht rn kt tinh c tinh khit cao, cn tp chtkhng thng hoa th nm li y bnh.

u im:n gin, thi gian ngn, tinh khit cao, gi thnh r.Nhc im:Trong thc t khng c nhiu cht thng hoa.

2.1.2. Tinh ch cht lng

2.1.2.1. Phng php chng cta. Khi nimChng ct l qu trnh lm bay hi cht lng, sau lm lnh v thu cht

lng c tinh khit cao hn.b. Cc phng php chng ct- Chng ct n ginTrong trng hp cn tinh ch mt cht lng, tch n ra khi tp cht rn

khng bay hi, ta ch cn tin hnh chng ct n gin ngha l chuyn n sangpha hi trong mt bnh ct c nhnh ri ngng t hi ca n bng ng sinh hnvo mt bnh hng khc.

- Chng ct phn onPhng php chng ct phn on dng tch hai hay nhiu cht lng c

nhit si khc nhau tan ln hon ton trong nhau da trn nguyn tc c sphn b khc nhau v thnh phn cc cu t gia pha lng v pha hi trng thicn bng ( cng nhit ). Nu hai cht lng khng tng tc vi nhau, c th

biu din s ph thuc ca nhit si ca cht lng v nhit ngng t ca hiph thuc vo thnh phn hn hp hai cht (hnh 2.1)

Hnh 2.1

T

TA

A BX2

X1

X1

T1

T2T

Thnh hn


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Qua hnh 2.1 nhn thy rng, bng cch lp i lp li nhiu ln qu trnhbay hi - ngng t, bay hi - ngng t li,... ta dn dn c th thu c cu t A

c nhit si thp hn dng gn nh tinh khit. V vy, ngi ta dng phngphp tinh luyn bng cch lp trn bnh ngng mt ct cao c nhiu a gip chovic ti to qu trnh bay hi - ngng t trn. Nh vy, cht lng A d bay hi dndn thot ln trn trng thi ngy cng tinh khit, cn cht lng B c nhit sicao hn, ngng t tr li bnh ct. C th dng loi ct lp y cc ng thu tinhhay s thay cho ct ni trn v hiu qu ca ct c tnh bng s a lthuyt.

Trong trng hp c tng tc yu gia hai cht lng (solvat ho hay thp) th thu c hai dng th biu din s ph thuc nhit si v ngng tvo thnh phn hn hp: mt dng vi nhit si ca hn hp ng ph cctiu(hnh 2.2a) v mt dng vi nhit si cc i (hnh 2.2b).

Trong trng hp hn hp ng ph c nhit si cc tiu (thp hn haicu t ban u), cng ln pha trn ca ct ct, hn hp hi v lng cng gn thnh

phn ca hn hp ng ph, trong bnh ct s cn li cht A hay B nguyn cht tytheo ta xut pht t hn hp c thnh phn pha bn tri hay bn phi hnh 2.2a.Trong hn hp ng ph c nhit si cc i, cng ln pha trn ca ct ct thcng giu cu t A hoc B, cn li trong bnh s l hn hp cng gn vi thang

phn ca hn hp ng ph (hnh 2.2b).

A B A B

Thnh phn Thnh phn

X0 X0

tA

tB

t

tA

tB

C

Ct

Hnh 2.2a Hnh 2.2b


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- Chng ct chn khng (hay gim p)Khi cn chng ct mt cht lng d b phn hu nhit cao, ngi ta

phi dng phng php ct chn khng, tc l dng bm ht gim p sut trnb mt cht lng. V cht lng s si khi p sut hi ring phn t n p sut khquyn, nn bng phng php ny, ngi ta c th gim c nhit si ca nmt cch ng k, trnh hin tng phn hu hay chy n. Nh phng trnhClapayron - Clausius, ngi ta c th tnh c s ph thuc ca p sut hi mtcht vo nhit . Tuy nhin, c th p dng qui lut thc nghim gn ng nhsau: khi p sut kh quyn trn b mt mt cht lng gim i mt na, nhit sica n b h thp i khong 150C.

- Chng ct li cun hi ncTa cng c th tinh ch mt cht lng khng ho tan trong nc, bng

phng php ct li cun theo hi nc h im si ca n.Phng php ny da trn nguyn tc: Khi hai hay nhiu cht lng khng

trn ln vi nhau nm trong mt hn hp, p sut chung p ca chng bng tng psut ring phn p1 + p2, ngha l n lun lun ln hn p sut hi ring phn catng cu t bt k no. Do , nhit si ca hn hp s thp hn nhit hnnhit si ca cu t si thp nht. T l hi ct sang bnh ngng (v s mol) s

bng t l p sut hi ring phn ca chng nhit si ca hn hp. Nh vy tac th tnh ton c lng nc cn thit li cun ht cht cn tinh ch.

Sau khi dng phng php ct li cun theo hi nc, thng ta phichit tch cc cht cn tinh ch ra khi nc bng mt dung mi thch hp, ri li

tin hnh ct phn on tch dung mi. Cui cng chng ly cht tinh khitbng bnh ct c gn nhit k di p sut thng hay gim p, vi s kim tranhit ca cht cn tinh ch.

- Phng php chitChit l dng mt dung mi thch hp c kh nng ho tan cht ang cn

tch v tinh ch tch cht ra khi mi trng rn hoc lng khc. Thngngi ta dng mt dung mi si thp v t tan trong nc nh ete, cloroform chit tch cht hu c t mi trng nc (cc cht hu c cn tinh ch nythng tan t trong nc hoc dng nh tng ln vi nc). Sau khi lc dungmi vi hn hp cht cn tinh ch v nc, cht s chuyn phn ln ln dung

mi v ta c th dng phu chit tch ring dung dch thu c khi nc.Bng cch lp li vic chit mt s ln, ta c th tch c hon ton cht cn tinhch vo dung mi chn, sau ct loi dung mi v ct ly cht tinh khit nhit v p sut thch hp.

Ngi ta cng thng chit mt cht t hn hp rn bng mt dung mihoc hn hp dung mi vi mt dng c chuyn dng c bit gi l bnh chaSoxhlet. Dung mi c un nng, cho bay hi lin tc chy vo bnh cha hnhp cn chit tch (thng c gi bng giy lc), n s ho tan cht rn cn tinhch v nh mt ng xiphng, dung dch chy xung bnh cu bn di, dung mi


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nguyn cht li tip tc c ct ln. Qu trnh c tip tc cho n khi s chittch c hon ton.

Phng php ny tit kim c dung mi v t hiu qu tng i cao.2.1.3. Phng php sc k

2.1.3.1. Khi nimPhng php sc k c Xvt pht minh ra tch cc cht bng hp ph

t u th k ny (1903), n nay tr thnh mt phng php tinh ch, nhtnh, nh lng rt quan trng trong ho hc hu c, c pht trin mnh m vc s dng rng ri trong hu ht cc phng th nghim hin i.

Nguyn tc chung ca phng php sc k nh sau: hn hp cht nghincu pha lng (dung dch) hay pha kh c cho i qua b mt cht hp ph

pha rn hay pha lng kh bay hi. Do kh nng tng tc vi pha tnh khc nhaunn cc cht khc nhau trong hn hp nghin cu chuyn ng vi vn tc khcnhau v dn c phn tch ra tng cu t ring bit.

2.1.3.2. Sc k ct (sc k hp ph)Trong phng php sc k ct, ngi ta dng cc ct thu tinh hay i khi

bng kim loi, c kch thc thng thng l 15x1; 25x2; 40x3 hoc 60x4 cm;dng cc cht hp ph dng bt, thng l nhm oxyt, silicagel, tinh bt, barisunfat... hoc mt cht bt k khc khng tng tc vi cht nghin cu v dungmi. Hn hp cht nghin cu c ho tan trong mt dung mi tr thch hp v

cho chy qua ct. Cc cht trong hn hp nghin cu dn dn tch khi nhau vchng chim cc v tr khc nhau trn ct hp ph. V lc u ngi ta tin hnhtrn ct th nghim vi cc cht mu, khi chng ta tch ra to thnh cc khoanhmu khc nhau trn ng hp ph nn phng php ny c gi l phng phpsc k. Sau ngi ta tch ring tng cht hoc bng cch ct ct hp ph thnhtng on ng vi tng cht, hoc lin tc thm dung mi, cc cht s ln ltc ra tri v thot ra bnh hng cc thi im khc nhau.

C th dng phng php ny tch cc cht khng c mu, nhng phidng cc cht ch th hay thuc th thch hp nhn bit khi no chng bt uthot ra bnh hng.

2.1.3.3. Sc k giySc k giy l mt dng c bit ca sc k phn b do Consden, Gordon

v Martin pht minh nm 1944. Pha tnh y l nc thm trn giy lc c bit(xenluloza tinh khit). Dung dch cht nghin cu c chm trn mt u ca digiy (cch mp giy chng 2,5cm) v mi git cch nhau chng 2cm. Ngi tathng nh ng thi c dung dch mu bit so snh. Sau u giy lcc nhng trong mt dung mi hay hn hp dung mi thch hp bo honc. Do lc mao dn, dung mi s thm dn ln giy sc k, ko theo chtnghin cu chuyn ng ln pha trn v to vt trn giy m ngi ta c th nhn


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bit c bng mt thng hoc bng cht ch th. T s Rtgia dch chuynca cht nghin cu v dung mi c gi l hng s sc k, hng s ny l i

lng quan trng c trng cho tng cht. thu c kt qu tch tt hn, ngi ta c th lp li thao tc trn vimt dung mi khc v theo chiu thng gc vi chiu chy ln trc (sc k phn

b hai chiu).Sc k giy thng dng nh tch cc cht, nhng cng c th dng

nh lng s b da vo m v tit din ca vt cht nghin cu.

2.1.3.4. Sc k lp mngPhng php ny c Izmailop v Schreiber ngh t nm 1938, c

Stan pht trin v hon thin (1955), khin n c ng dng rt rng ri.Ngi ta trng mt lp mng cht hp ph (Al2O3, silicagen) ln mt tm

knh kch thc khong 10x12 cm hoc 20x20 cm, chm mt git cht nghin culn mt u bn (cch mp khong 2cm) ri cho dung mi chy nh sc k giy.

Phng php sc k lp mng thng cho hiu qu tch cao, thi gianngn, lng cht t, thng c dng nh tnh v tch cc hp cht thinnhin. N cng c cc nh ho hc tng hp s dng thng xuyn nhanhchng phn tch cc cht thu c trong phn ng.2.1.3.5. Sc k kh lng

Nhng nm gn y sc k kh lng c pht trin mnh m, m ra khnng ln trong phn tch v tch cc hp cht d bay hi. Phng php thngthng l cho vi microlit cht lng phn tch vo thit b bay hi ri dng dng

kh mang (thng l He) li cun hi ca chng qua mt ng di nung nng npy mt cht rn xp (gch chu la tn nh, nhm oxyt, silicagel, than hottnh...) c tm bng cht lng kh bay hi nh du silicon, polyetylen glycol,cc este si cao...Khi xy ra s phn b cc cht gia pha lng v pha kh, ngthi ch cn c s khc nhau nh trong s phn b ny gia cc cu t trong hnhp cng phn tch hon ton cc cht lng trong hn hp, v n c lp ilp li nhiu ln trong ng di. Ngi ta thng nhn bit tng cht thot ra cuing bng cch o s thay i dn nhit ca kh thot ra. Tuy nhin vic phthin mt pic trong s sc k kh mi l iu kin cn, nhng cha v tinhkhit ca mt cht, phng php sc k kh vn rt hu ch khi phn tch mt

lng nh hn hp cng nh tch v tinh ch cc cht.Cn nhn mnh rng, trong phng php sc k, ni chung cu trc phn tca cc hp cht c nh hng ln n cn bng hp ph, cng nh h s phn bca chng gia cc pha, do lin quan cht ch n hng s Rt. V vy kt qu

phn tch sc k cng cho ta thy nhng thng tin b ch v cu trc ca hp cht.Sau qu trnh tinh ch, ta cn kim tra tinh khit ca hp cht thu c

bng cch o nhit nng chy (i vi cht rn) hoc nhit si (i vi chtlng) hoc o t khi, ch s khc x, chp ph...Mt cht c coi l tinh khitnu qua nhiu ln tinh ch, cc hng s vt l ca n khng thay i.


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2.2. Cng thc phn t hp cht hu c xc nh c cng thc phn t cc cht hu c, ngi ta tin hnh

xc nh cc thnh phn nguyn t v khi lng phn t ca chng.2.2.1. Phn tch nguyn t

Cc cht hu c ngoi cacbon cn thng c hydro, oxy, nit, halogen, luhunh,... xc nh s c mt v hm lng ca chng, ngi ta s dng cc

phng php nh tnh v nh lng ring.

2.2.1.1. Xc nh cacbon v hydroS c mt ca cacbon v hydro trong mt hp cht thng c xc nh

bng cch t chy hp cht trong oxi, vi xc tc l CuO:

CxHyOz + (x + y/4 - z/2) O2 x CO2 + y/2 H2O

CO2thot ra c nhn bit bng phn ng lm c nc vi trong:

Ca(OH)2 + CO2 CaCO3 + H2O

H2O c nhn bit bng cch ngng t trn phn lnh ca ng t haybng CuSO4khan.

nh lng cacbon v hydro, ngi ta t chy mt lng cn chnh xccht nghin cu bng dng oxy c mt CuO trong ng thch anh, ri hp th hi

nc thot ra bng perclorat magie (MgClO4); CO2 hp th bng bng tm st(NaOH). Cc cht hp th ny ng trong ng ch U v khi lng ca chngc cn chnh xc trc v sau khi th nghim kt thc. Hiu s khi lng giahai ln cn cho ta bit khi lng H2O v CO2b hp th.

Nu trong thnh phn cht nghin cu c halogen, lu hunh, nit, chngc th to ra cc oxit ca nit, ca lu hunh, halogen v cc oxit halogen hydricv chng c th nh hng n kt qu cn cc ng hp th. loi tr chng,trong ng nung phn cui, ngi ta dng cc si bc gi halogen v oxit luhunh, dng P2O5 phn hu oxit nit.

2.2.1.2. Xc nh nit xc nh s c mt ca nit trong hp cht nghin cu, ta c th tnng mu th vi natri kim loi, nit cng cacbon trong mu th s chuyn thnh

NaCN, ho tan sn phm to thnh trong nc ct, lc ly dung dch; thm lnlt cc ion Fe2+, Fe3+, axit ho s to thnh kt ta mu xanh:

6CN- + Fe2+[Fe(CN)6]4-

4Fe3+ + 3[Fe(CN)6]4-Fe4[Fe(CN)6]3

mu xanh


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nh lng nit, ngi ta dng phng php Dumas hoc Kjeldahl.Nguyn l ca phng php Dumus l oxy ho hp cht hu c bng CuO

ri li cun sn phm bng mt dng CO2 tinh khit. Nit trong cht hu c schuyn thnh N2t do. Ta c th thu N2thot ra bng mt buret p ngc trongchu cha dunh dch KOH m c. H2O s ngng t trong dunh dch; CO2honton b hp th bi KOH; N2thot ln c v ta c th o c th tch ca nmt cch d dng.

Phng php Kjeldahl tuy khng ph bin bng phng php Dumus songtrong nhiu trng hp cng rt thun tin, n cho php xc nh nhanh hmlng nit trong mu th. Bng cch v c ho hp cht nghin cu khi nungnng trong H2SO4m c c xc tc selen (khi cn c th thm cht oxy ho) tachuyn nit thnh mui amon sunfat, sau kim ho dung dch thu c ri licun NH3theo hi nc sang mt bnh khc v chun lng NH3to thnh.

2.2.1.3. Xc nh halogenS c mt ca halogen trong hp cht hu c c xc nh bng cch tm

mu giy vo si dy ng ri t, nu hp cht c cha halogen s to ra ngnla mu xanh lc.

Ngi ta nh lng halogen bng cch oxy ho mu cht trong bnh chaoxy nguyn cht, c xc tc Pt, khi s to halogenua hydro, hp th bng dungdch HNO3v sau xc nh bng phn ng nitrat bc:

AgNO3+ HX AgX+ HNO3

Bng cch so c hoc chun lng Ag+d, ngi ta tnh c hmlng halogen trong mu cht nghin cu.

2.2.1.4. Xc nh lu hunhKhi un chy hp cht hu c vi kim loi, lu hunh s chuyn thnh

Na2S, sau ta c th d dng nhn bit c bng cch phn ng to kt ta PbShay Ag2S:

Pb(NO3)2+ Na2S PbS+ 2NaNO3

nh lng lu hunh, ngi ta oxy ho mu cht hu c bng HNO 3bc khi trong ng hn kn 200 300oC, sau vi gi lu hunh trong mu chts chuyn ho thnh H2SO4, ta c th nh bng phn ng vi BaCl2, ri xc nhlng BaSO4bng phng php trng lng:

H2SO4+ BaCl2= BaSO4+ 2HCl

2.2.1.5. Xc nh cc nguyn t khc


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Ngoi cc nguyn t k trn, trong mt s trng hp chy hu c c thcn cha P, Si, mt s kim loi khc...

Ta cng oxy ho hp cht hu c bng HNO 3bc khi trong ng hn knhoc nung chy n vi hn hp NaNO3 v Na2CO3. Cc nguyn t ni trn schuyn ho thnh cc hp cht v c tng ng (thng vi ho tr dng caonht), sau ta nh lng chng bng cc phng php v c thng thng.

2.2.1.6. Xc nh oxyHm lng oxy trong cc hp cht thng c xc nh mt cch gin

tip, tc l ta ly khi lng mu em t tr i khi lng tng cc nguyn tva xc nh theo cc phng php trn, hoc ly 100% tr i hp phn ca ccnguyn t khc.

Ta cng c th xc nh mt cch trc tip bng cch chuyn oxy trong hpcht hu c thnh CO ri oxy ho bng I2O5:

5CO +I2O55CO2+ I2

Chun lng I2, CO2 c gii phng ra hoc chun lng I2O5d,ta tnh c lng CO hnh thnh.

Tm li, nh nhng phn tch ch to cc k chnh xc, nh nhng thit bphn tch ngy cng hon thin, ngi ta c th tin hnh phn tch vi lng hocbn vi lng, vi nhng cht nh (vi mg) cng cho ta kt qu ng tin cy. Tnhng nm 60, ngi ta pht hin v s dng cc phng php siu vi lng,

ch cn cn mu cht (trn cn in t t ng) cn cc sn phm t chy cxc nh bng nhng thit b tinh vi trn c s o dn nhit ca cc cht khnh b pht in etect. Vi phng php ny, ngi ta c th xc nh ngthi C, H, N hon ton t ng trong vng 10 pht, lng mu ch cn khong 1mg.

2.2.2.Thit lp cng thc tng qut ca hp chtSau khi xc nh thnh phn khi lng (hoc thnh phn trm khi lng)

ca tng nguyn t trong cht nghin cu, bng cch chia cho nguyn t lngca cc nguyn t tng ng, ta s c t l gia s nguyn t tng nguyn t

trong phn t, t thit lp c cng thc tng qut ca cc cht cho didng (CxHyOzNt)nV d:

t chy 1,5 mg mt cht A to thnh 0,9 mg H2O; 1,76 mg CO2v 0,224ml N2 (ktc). Ta tnh khi lng tng nguyn t trong mu cht nh sau:

0,9 mg H2O 0,0009/ 18 ptg (0,0009/18) x 2 = 0,0001g H = 0,1 mg H1.76 mg CO20,00176/44 ptg (0,00176/44) x 12 = 0,00048 g C = 0,48mg C0,224 ml N20,224/22,4 ptg (0,224/22,4) x 28 = 0,28 mg N


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Lng oxy: mO= 1,5 -(0,48+0,1+0,28) = 0,64 mg

Ta c:CxHyOzNt+ (x+y/4-z/2) O2xCO2+y/2 H2O + t/2 N2

V x : y : z : t = 0,48/12 : 0,1/1 : 0,64/16 : 0,28/14 = 2 : 5 : 2 : 1Vy cng thc tng qut ca cht nghin cu l (C2H5O2N)n.

xc nh n ta phi xc nh khi lng phn t cht cho hoc i khikhng thc hin c trong iu kin th phi bin lun.

2.2.3. Xc nh khi lng phn t ca mt cht tm c cng thc nguyn (cng thc phn t) ca mt hp cht, ta

phi xc nh khi lng phn t, hay ni chnh xc hn l xc nh phn t gamca cht nghin cu. C nhiu phng php xc nh phn t lng.

a. Nu mu cht nghin cu l cht lng d bay hi, ta cho bay hi nhit thch hp, o th tch hi iu kin ri tnh phn t lng ca n theo

phng trnh:

pV = nRT = (m/M)RTM = mRT/pV

Trong :

p - p sut;V - th tch hi cht nghin cu;m - khi lng cht bay hi;T - nhit tuyt i;R - hng s kh.

b. Nu o c t khi hi ca cht cho i vi mt cht kh no , tac th tnh c phn t gam ca n mt cch d dng.

V d, hi cht A nng gp 25 ln H2th phn t lng ca n phi lM = 25 x 2 = 50.

c. Da vo nh lut RaoultDung dch mt cht kh bay hi trong mt dung mi no c lun c

nhit si cao hn, nhit ng c thp hn so vi dung mi nguyn cht v tng im si hay h im kt tinh lun t l vi nng cht tan.

t = KC

K - h s t l, c gi l hng s nghim si hay nghim lnh, c trngcho tng loi dung mi;


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C - nng mol/l hay khi lng mol phn t/1000 g dung miBng cch o mc tng nhit si (phng php nghim si) hoc mc

h im kt tinh (phng php nghim lnh) ca dung dch cht nghin cu trongdung mi cht thch hp, ta d dng xc nh c nng cht tan v do xcnh c phn t gam ca chng.

Ngi ta hay dng campho lm dung mi, v hng s nghim lnh ca nkh cao (khi ho tan mt phn t gam cht tan trong 1000 g campho, im ngc h i t =37,7oC.

d. Cc phng php khcBng cch tng t, ngi ta cng c th o p sut thm thu ca dung

dch cht tan, o nht ca dung dch hoc bng phng php khi ph, t xc nh c khi lng phn t cht cho. Nu bit r s nhm chc trongmt phn t cht nghin cu, bng cch xc nh s nhm chc cng cho php xcnh phn t lng ca chng.

V d, 0,92 g mt alcol n chc tc dng vi mt lng d Na cho 0,224 lH2(ktc) th phn t lng ca alcol phi l:

0,92/ (0,224 x 2)/22,4 = 46

2.2.4. Thit lp cng thc nguyn ca mt hp chtSau khi xc nh c cng thc tng qut ca cht nghin cu khi lng

phn t ca n, ta d dng tm ra c tr s ca n v do thit lp cng thc

nguyn ca hp cht.V d, lp c cng thc tng qut ca cht A di dng (C 2H5O2N)n

nh v d trn, ng thi bng mt trong cc phng php va nu ta xc nhc phn t lng ca cht A l 75, ta tnh c:

(2 x 12+5 x 1+2 x 16+1 x 14)n = 7575n = 75 n = 1

Vy cng thc nguyn ca A phi l C2H5O2N.

Tuy vy, nhiu khi trong iu kin thc nghim khng cho php ta thc

hin tt c cc bc trn, c ngha l phi gii bi ton tm cng thc nguyn khis phng trnh ton hc lp c it hn s n s, trong khi trng hp ny taphi bin lun. Phng php bin lun phi da vo c im ca hp cht cho xc nh tr s n trong cng thc tng qut, hoc da vo cc bt phng trnh

phn nh mi tng quan gia s nguyeen t ca cc nguyn t c bn.

V d, mt hydrocacbon c t khi i vi hydro l 21. Hy tm cng thcca n.

Ta c khi lng phn t l 21x2 = 42. Nu gi cng thc ca hydrocacbon l CxHy, ta c:


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12x + y = 42Suy ra: 12x < 42

Hay : x < 3,5Mt khc CxHy l hydrocacbon nn s nguyn t H trong phn t khngvt qu 2x + 2, ngha l:

y 2x + 242-12x 2x + 2

40 14x2,8 x

Kt hp vi lp lun trn, ta c 2,8 x


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H C

H

H

C

H

H

C C

H

H

H

H

C

H

H

H

H C

H

H

C

H

H

C

H

CH3

C

H

H

H

H C

H

H

C

CH3

CH3

C

H

H

H

Khi s lng ca nguyn t cacbon trong phn t hyrocacbon tng ln ths lng cc ng phn cu to tng rt nhanh. V d C6 c 5 ng phn, C7-9, C8-18, C20-366 319, C40-62.491.178.805.831 ng phn.

Mt loi ng phn cu to khc xut hin khi phn t ca cc hp chthyrocacbon c cha cc lin kt bi. V d hp cht hyrocacbon C4H8 tn tidi 2 dng ng phn sau:

H C

H

H

C

H

H

C C

H H

H H C C C C H

H

H

H H H

H

v

Phn loi: Loi ng phn ny thng gp cc dng sau:- ng phn v mch cacbon, ngha l ch khc nhau v cch sp xp mch

cacbon:

CH3CH2CH2CH2OH CH3CHCH2OH

CH3

ancol n - butylic ancol isobutylic

- ng phn v v tr ca nhm chc. Cc hp cht ny c cng nhm chc

nhng khc nhau v s phn b v tr ca nhm chc:

CH3CHCH2CH3

OH

CH3CH2CH2CH2OH

Butan-2-olButan-1-ol

- ng phn v nhm chc:CH3CH2CH2CH2OHCH3CH2-O-CH3

ete ancol

- ng phn v cch chia on mch ca nhm chc:


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CH3C-O-CH2CH2CH3

O

CH3-O-C-CH2CH2CH3

O

axetat n - propyl butyrat metyl

Hai cht u thuc este, nhng xut pht t hai cp axit v ancol khc nhau,axetat n - propyl hnh thnh t CH3COOH + CH3CH2CH2OH, cn este butyratmetyl hnh thnh t CH3CH2CH2COOH + CH3OH.

b. ng phn hnh hcKhi nim: L ng phn cu hnh do s sp xp khc nhau ca cc nhm

th 2 bn ni i hay mt phng vng no. S sp xp cc nhm th hai bn ni

i thc cht l hai bn mt phng . Mt phng v mt phng vng l nhngmt phng c nh. Nu hai nhm th ging nhau hay gn ging nhau cng phaca mt phng gi l ng phncis, khc pha l ng phn trans.

V d:

C C

CH3

HH

H3C

C C

H

CH3H

H3C

cis-but-2-en trans-but-2-en Cl

H

H

Cl

H

H

H

Cl

H

Cl

H

H

cis-icloxyclopropan trans-icloxyclopropan

Cch qui nh v tr hai nhm th ging nhau trn y ch l trng hp cbit trong cch qui nh tng qut v v tr ca 2 nhm th trong mch chnh.

V d:

CH3 > H

C2H5 > CH3

C C

C2H5

HH

H3C

C C

CH3

C2H5H

H3C

iu kin cn v xut hin ng phn hnh hc


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27

- iu kin cn: Phn t phi c ni i hay vng no nm trn mt mtphng.

- iu kin : 2 nhm th mi cacbon ni i hay vng no phi khcnhau.

C C

c

d

a

b

Phn loi: c 3 loi- ng phn cis trans

+ ng phn cis-trans xut hin cc ni i C-C khi c hai nguyn thoc nhm nguyn t nm cng pha hoc khc pha ca mt phng .

C C

CH3

HH

H3C

C C

H

CH3H

H3C

cis-2-buten trans-2-buten

+ Trng hp phn cng nhc ca phn t l mt ni n hoc mt phnvng trong cc hp cht vng:Dn xut c 2 ln th:Xiclopropan c 2 ng phn hnh hc

Cl

H

H

Cl

trans

Cl

H

Cl

H

cis

CH3HOOC CH3

HOOC

transcis Xiclobutan c 4 ng phn hnh hc

a b

c d


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Cl Cl

Cl Cl

cis trans

Cl

Cl

cis

Cl

Cl

trans

Xiclopentan c 5 cu trc

a b c d e

Trong b,c,d,e l ng phn hnh hc ng thi nu 2 nhm th gingnhau th c, d l hot ng quang hc cn nu khc nhau th c b,c,d,e u hotng quang hc.

Xiclohexan: cis-trans ca 1,2; 1,3; 1,4

cis-1,2 cis-1,3

cis-1,4

trans-1,2trans-1,3

trans-1,4

Nhng hp cht c nhiu cnh v khng phng c s ng phn hnh hctng ln nhiu v tng s ng phn v tr v s nhm th c th c. Quan trng lloi hp cht hexacloxyclohexan v loi inosit c 8 ng phn cis-trans, tong

c 7 dng meso v mt dng nghch quang:


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29

X

XX

XX

X X

X

X

XX

X X

XX

XX

X X

X

X

XX

X X

X

X

X

XX

XXX

XXX

X

X

X

X

X

X

X X

X

X

XX

cis-inosit epiinosit mesoinosit mucoinosit neoinosit

D,L-inosit

alloinosit

spiloinosit

X=OH; Cl

Cc d vng:

NH

CO NH

CO

H

HOOC

COOH

H

NH

CO NH

COH

HOOC

H

COOHtrans cis

Cc hp cht vng ngng tVng 3 cnh ngng t vi vng 4,5,6 cnh ch c ng phn cis

1

2

1cis-bixyclo(2,1,0)pentan

Vng 4 cnh ngng t vi vng 5,6 cnh ch c ng phn cis cn ngng tvi vng 7 cnh th c ng phn cis-trans:

cis-bixyclo(4,2,0)octan cis-bixyclo(5,2,0)nonan trans-bixyclo(5,2,0)nonan

Vng 5 cnh ngng t vi vng 5 cnh, vng 5 cnh ngng t vi vng 6cnh c ng phn cis-trans


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30

cis-bixyclo(3,3,0)octan trans-bixyclo(3,3,0)octan cis-hidrindan trans- hidrindan

Vng 6 cnh ngng t vi vng 6 cnh c dng phn cis-trans

Cis-ecalin trans-ecalin

- ng phn syn anti

Danh php Syn-anti: Dng cho ni i

C Y

c mt cp in t khngphn chia nh i vi loi hp cht andoxim, xetoxim khng i xng, hidrazon,hp cht azo c lin kt C=N, N=N. (syn-: cng pha, anti-: khc pha).

V d: CH3- CH = N - OH

C N

OH

H

H3C

C N

H

H3C

OH

Syn- anti-

N

N

C6H5

C6H5

N

N

C6H5

C6H5

syn anti

- ng phn E - ZTrong trng hp khng dng c danh php cis - trans th dng danh

php chung gi l danh php E-Z.

..


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31

Danh php E-Z da trn tnh hn cp ca nguyn t nh vi cacbon. Nhmth c nguyn t c s th t nguyn t cao hn (hay c khi lng nguyn t

hoc phn t ln hn) th c tnh hn cp cao hn. Nu hai nhm th c tnh hncp cng pha ca mt phng gi l ng phn Z, khc pha l ng phn E.

+ Nhm th c nguyn t nh vi C lai ha sp2c s th t hay in tchht nhn ln hn s hn cp hn:

Br > Cl > S > P > F > O > N > C > H

+ Nu cc nguyn t lin kt trc tip ging nhau th xt lp th hai:

CH(CH3)2> CH2CH3> CH3(RO)3C > (RO)2CH > ROCH2

+ Cc nguyn t c cha lin kt bi c tnh bi ln:

HC=O > CH2OH ; C6H5> (CH3)2CH ; C N > CH2NH2

+ Trong s cc ng v, nguyn t c s khi ln hn l hn cp hn D > HV d:

C C

NO2

H

Br

H3C

C C

H

NO2

Br

H3C

Br > CH3 , NO2 > H

(Z)-2-Brom-1-nitropropen (E)-2-Brom-1-nitropropen

Tnh cht ca ng phn hnh hc+ bn tng i ca ng phn hnh hc: tnh bn ca cc anken tng

theo mc ankyl ha ca etylen:R2C=CR2> R2C=CHR > R2C=CH2

RCH=CHR > RCH=CH2>CH2=CH2

ng phn hnh hc ni chung th ng phn trans bn hn cis do ngphn cis c s y ln ca cc nhm th gn nhau hn.

+ Cc ng phn hnh hc c nhiu tnh cht khc nhau r rt, v d 1,2-icloetilen.


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cis transKhong cch 2 Cl 3,7A0 4,7A0

1,89D 0,0Dt nc -80,5 C -50 Ct s 60 C 48 C

+ S ng phn ha hay chuyn ha ln gia cis-transPhn ng c in chuyn ha gia ng phn cis-trans l phn ng

quang ha. Khi chiu sng, nng ng phn cis trng thi dng quang ha lln hn trng thi c bn. Nh vy, s chiu sng l phng php chuyn ng

phn trans thnh cis.Phn ng chuyn ha cis-trans c th thc hin bng phn ng ha hc qua

nhiu giai on phn ng:

C C

R R

H H

RCOOHC CH

R R

H H

O

C CH

R R

H H

O

PR3

SN2

C C

H H

R

R

O-

PR3

C C

H O-

R

PR3

H

RR3PO

-C C

R H

H R

cis

trans

Giai on u l phn ng epoxy ha, sau l phn ng th SN2 vi s tncng ca photphin. c phn ng tch cis, tc nhn th SN2phi quay xungquanh lin kt C-C.

Nu xut pht ban u t trans, qua qu trnh trn thu c cis. Nh vyqu trnh trn dng chuyn ha cis trans ca anken. iu ny gii thch tisao c 2 nguyn t cacbon v hidro m to nn v s cc phn t hp cht hu c.

c. ng phn khng gian- ng phn quang hc


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33

Khi nim: Nhng hp cht c cu trc v tnh cht vt l, ho hc gingnhau nhng khc nhau v kh nng quay mt phng nh sng phn cc gi l ng

phn quang hc.nh sng l dao ng sng ca trng in v t. Khi mt electron tngtc vi nh sng th c dao ng theo tn s ca nh sng theo hng ca trngin. nh sng thng c vect trng in ca sng nh sng trong tt c cchng ca mt phng. nh sng phn cc c vect ca trng in ca tt c ccsng nh sng trong cng mt mt phng, gi l mt phng phn cc.

nh sng phn cc thu c khi cho nh sng thng i qua lng knhphn cc:

C mt s cht hu c (v c mt s cht v c) c kh nng lm quay mtphng phn cc khi cho nh sng phn cc i qua. Kh nng gi l tnh quanghot, cn nhng cht c kh nng gi l cht quang hot. Trong s nhng chtquang hot c mt s khng nhiu lm ch th hin kh nng lm quay mt phng

phn cc khi cn trng thi tinh th (tinh th bt i), v d: tinh th ca cc chtNaCl, ZnSO4. Cn mt s ln cht khc li c tnh quang hot khi th hi hay

nh sng thng nh sng phn cc

nh sng thng nh sng phn cc

Phn cc k


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34

trong dung dch. loi cht quang hot va ni, tnh quang hot khng phi docu trc tinh th m do cu trc ca nhng phn t ring r.

o kh nng lm quay mt phng phn cc ( quay cc) ca cc chtquang hot ngi ta dng phn cc k ghi ly gc quay . i vi mt chtquang hot ngi ta thng dng i lng quay cc ring []. quay ccring ca mt cht trong dung dch c tnh theo cng thc sau:

aL

Vt.

.0

Trong : : Gc quay quan st c i vi mt dung dch c b dy nh sng i

qua l d (dm) cha a (g) cht quang hot trong V (ml) dung dch. Vic thchin t0, vi nh sng c di sng .

Gc quay ca mt cht quang hot khng nhng ph thuc vo bn chtho hc ca cht , bc sng ca nh sng phn cc, b dy ca dung dch chtquang hot, nhit khi o, m cn ph thuc vo nng v bn cht dung mi.Cho nn khi vit quay cc ring phi ghi c th. V d:

025 18D (C = 15 nc)

Nh th c ngha l quay cc ring ca cht quay v bn tri 180, nng 15g trong 100 ml dung dch nc, nhit khi o l 250, b dy dung dch

1dm, nh sng c dng l nh sng D ca natri vi bc sng 589nm.iu kin xut hin ng phn quang hc+ iu kin cn: Phi c trung tm bt i (nguyn t bt i, phn t bt

i hay tinh th bt i)+ iu kin : Phi c phn b theo cng thc chiu Fis.iu kin cn v xut hin tnh quang hot l khi phn chiu m hnh

ca hp cht qua mt mt phng ta c m hnh khc khng ng nht vi n,ngha l khng th ch bng chuyn ng tnh tin v quay m c th a c haim hnh lng kht vo nhau c. Ni cch khc, xut hin c hin tngquang hot, phn t phi khng lng kht c vi nh gng ca n, tng tnh quan h gia hai bn tay ca mt ngi bnh thng. Tnh cht c gi ltnh khng trng vt - nh(chirality). Khi c hin tng ny, s xut hin hai dngng phn i xng nhau, khng lng kht vo nhau c nh hnh a.1


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35

Hnh a.1: Hai dng ng phn i xng nhau

Hai ng phn ny c kh nng lm quay mt phng nh sng phn ccnhng gc c tr s nh nhau nhng theo chiu ngc nhau. l hai cht iquang.

Nguyn t cacbon bt iTrong mt hnh t din u c mt tm i xng, bn trc i xng v su

mt phng i xng.Nu ta thay th tt c bn nguyn t hydro trong phn t CH4 bng bn

nguyn t hay nhm nguyn t ging ht nhau th cc yu t i xng vn cnnguyn vn. Nhng nu thay th mt hay nhiu nguyn t hydro trong CH4bngnhng nguyn t hay nhm nguyn t khc nhau th cc yu t i xng s b vi

phm.V d: Th mt nguyn t H bng Br th ch cn mt trc i xng v ba

mt phng i xng, th 3 nguyn t H bng 3 nguyn t khc nhau th s khngcn mt yu t i xng no c.

Khi trong phn t c nguyn t C nh vi 4 nguyn t hay nhm nguynt khc nhau Cabcd s xut hin hai dng ng phn i xng nhau qua mt

phng nh vt vi nh trong gung (hnh a.1) v c tnh quang hot. Nguyn t Cgi l nguyn t C bt i, phn t Cabcd l phn t bt i.

V d:

C*

a

b

c

d C*

H

H3C

OH

COOH C*

H

Cl

I

SO3H C*

F

Cl

Br

I

Trong trng hp hai nguyn t ng v nh vo mt nguyn t C cngvi hai nhm nguyn t khc na, nguyn t C cng l C bt i, cho nnnhng hp cht nh trong v d di y cng c th l nhng cht quang hot:

a

d c

b

a

c d

Mt phng gng


36/179

36

C*

H

C6H5

D

CH3 C*

H

H3C

OH

CD3

biu din nguyn t cacbon t din trong cc phn t kiu Cabcd ta cth dng cc cng thc khc nhau hnh a.2. l cc cng thc t din (1), Fis(2) v (3), phi cnh (4) v phi cnh kt hp vi Fis (5).

Trong cc cng thc , nt lin biu din lin kt nm trn mt phnggiy, nhng ng chm nh hoc ng gch ngn dn dng ch nhng lin

kt hay ng ni hng v pha di mt phng giy (i xa pha ngi quan st),cn cc ng m hnh tam gic ch nhng lin kt hng t mt phng giyv pha ngi quan st (i gn pha ngi quan st) :

c

a b

d

a

c

b

d

(4) (5)

Quy tc chiu Fis+ Mch chnh biu din cnh nm dc.+ Nguyn t hoc nhm nguyn t c s oxi ho cao th c biu din

pha trn, ngc li th biu din pha di.+ Qui c: Cc nhm nguyn t ng k ngang (a v b) pha gn

ngi quan st, cn cc nhm nguyn t ng dc (c v d) pha xa hn.Mun chuyn cng thc hnh t din sang cng thc Fis ta dng phng phpchiu cc nhm nguyn t ca t din ln mt phng giy. Khi y cn ch l t

b

d

c

a

c

a

d

b

c

a

d

b

(1) (2) (3)


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37

din phi c phn b nh th no mt cnh nm ngang ca t din gnngi quan st.

V d:

+ Ta c th bin i cng thc Fis theo cc cch khc nhau, khi y tutng trng hp m cu hnh vn c bo ton hay b nghch o (quay cuhnh).

i ch bt k hai nhm th no C cng lm quay cu hnh v nh vys sinh ra mt dng khc ca phn t ban u.

V d:

CHO

CH3

OHH

CHO

CH3

HOH

b

d

c

a

c

a bd

c

a b

d

CHO

CH2OH

H OH

Dng D

CHO

CH2OH

OH H

Dng L

OH

CH2OH

OCH H

Dng D

CH3 CHOH* CH2OH+1-3


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38

Nu dch chuyn ng thi ba nhm th theo chiu kim ng h hoctheo chiu ngc li th cng thc Fis vn gi nguyn ngha, tc l cu hnh

c bo ton.V d:

CHO

CH2OH

H OH

Dng D

Khng c a cng thc Fis ra khi mt phng giy, cng khngc quay cng thc trn mt phng nhng gc 900hay 2700(v s quay cu hnh)nhng c th quay 1800(cu hnh khng i).

V d:

CHO

CH2OH

H OH

Dng D

CHO

CH2OH

OHH

Dng D

Quay 1800

CH2OH

CHO

HO

Dng D

H

CHO

H

OH CH2OH

Dng D

Quay 900

H

CHOHOCH2

OH

CHO

HHO

CH2OH

Dng L


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39

biu din hai hay nhiu nguyn t cacbon t din k tip nhau ta cngc dng cng thc t din hay cng thc Fis

V d: Vit ng phn quang hc ca : HOOC-CHOH-CHOH-COOH

Phn loi ng phn quang hc+ Cp i quang

V d: Andehit glixeric HOCH2-CHOH-CH=O

+ Tnh cht ca mt cp i quangGing nhau: Hai cht i quang c cc tnh cht vt l v ho hc bnh

thng ging ht nhau.Khc nhau: Chng khc nhau du ca nng sut quay cc (= +: quay

sang phi; = - : quay sang tri) v hot tnh sinh hc ( tng tc vi tc nhn

CHO

CH2OH

H OH

Andehit D (+) glixeric

CHO

CH2OH

OH H

Andehit L (-) glixeric

COOH

COOH

H

H

OH

OH

COOH

COOH

HO

HO

H

H

COOH

COOH

H

HO

OH

H

COOH

COOH

HO

H

H

OH

ng phn mz Hai ng phn i quang

Hai ng phn khng i quang


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40

c tnh quang hot). Nhng s khc nhau ny bt ngun t s khc nhau v cuhnh.

+ Tnh cht ca cp ng phn quang hc khng i quang (ng phn lpth ia)Ging nhau: C tnh cht vt l v ho hc bnh thng ging ht nhau.Khc nhau: Gi tr gc quay cc khc nhau nhng c th giing nhau hoc

khc nhau v du.- ng phn mzL ng phn c yu t i xng ni phn t, c c im gc quay cc

ring = 0, l ng phn lp th khng quang hot (do s b tr ni phn t).

V d:

- Bin th RaxemicV d:

Thng thng trong t nhin cng nh trong cc qu trnh ha hc, ngita hay gp hai cht i quang ca mt cht tn ti dng tp hp ng phn t(cu to ca tp hp cha tht r rng) gi l bin th raxemic, k hiu bng du( ) hay ch D, L hoc d, l. V d : andehyt ( ) glyxric. Tt nhin phi hiu rngkhi nim bin th raxemic l mt khi nim c tnh cch thng k, khng dng ch cc phn t ring r m ch mt tp hp ln cc phn t.

Bin th raxemic khng c tnh quang hot v y c s b tr nhau vnng sut quay cc gia hai cht i quang (= 0).

COOH

COOH

H

H

OH

OH

COOH

COOH

HO

HO

H

H

Axit mztactric

CN

CH3

OHH

CN

CH3

HHO


41/179

41

Thng thng cc trng thi kh, lng hay dung dch, bin th raxemic cth c coi l hn hp ng phn t gn nh l tng ca hai cht i quang cho

nn n c tnh cht vt l ging nh cc cht i quang to nn n nh t

0

s, t khi,chit sut, quang ph hng ngoi trng thi lng hay dung dch,...Ch : H thng k hiu D-L c nhng hn ch nht nh nn hin nay

ngi ta dng ph bin h thng R-S ch cu hnh.S ng phn quang hc ca mt hp cht l: N = 2n trong n l s

nguyn t C bt i. Tuy nhin i vi cc cht c s i xng ring trong phn tth s ng phn lp th t hn 2n.

- ng phn cu dngKhi nim+ Cu dng l nhng dng cu trc khng gian sinh ra do s quay xung

quanh mt hay vi lin kt n m khng lm t nhng lin kt ny.+ ng phn cu dng (ng phn quay) l nhng cu dng tng i bn

ca phn t.iu kin c ng phn cu dng+ iu kin cn: C lin kt n C - C.+ iu kin : Phi c m t bng cng thc Niumen hoc biu din

di dng phi cnh.Phn loi+ Cu dng ca etan v cc hp cht kiu X3C - CX3Dng che khut: Dng c th nng cao nht, cu dng ny khng bn.

H

H

H

H

H

HH

H

H

H

HH

Dng xen k: Dng c th nng thp nht, cu dng ny bn.

H

H

H

H

H

H

H

H

H

HH

H

S ng phn cu dng: N =n

0360vi n l gc quay. Nh vy ta s c

v vn dng hnh hc khc nhau, trong c hai dng ti hn l dng che khut vdng xen k.


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42

Biu din th nng theo gc nh din ( n = 600) ta s c gin th nng:

H

H

H

H

HH

H H

H

H

HH H

H

H

H

HH

H H

H

H

HH

H

H

H

H

HH

H H

H

H

HH

H

H

H

H

HH

Gin trn c dng hnh syn, vi 3 cc i bng nhau v 3 cc tiu bngnhau ng vi chnh lch v nng lng l 2,8 kcal/mol.

Cu dng v gin th nng ca cc hp cht khc kiu X3C - CX3tngt etan.

+ Butan v cc hp cht kiu XCH2 CH2Yi vi phn t n-butan CH3-CH2-CH2-CH3khi quay quanh lin kt C-C

xut hin 2 cc i nng lng ng vi hai dng che khut: che khut ton phnv che khut mt phn v 2 loi cc tiu nng lng ng vi 2 dng xen k. Ngita phn bit 2 dng xen k: anti (hay transoit) v syn (cisoit). Dng anti tng i

bn hn dng syn, chnh lch nhau khong 0,7 kcal/mol. Tng tc gia 2 nhmCH3- lm cho dng syn km bn, gi l tng tc syn. nhit thng, dnganti chim t l gp i dng syn.

i vi dn xut 1,2-ihalogen ca etan nh: 1,2-icloetan; 1,2-ibrometan.ta cng thy hin tng tng t nh n-butan. Kt qu nghin cu cho thyrng trong dung dch CCl4 25

0C, 1,2-iclo etan tn ti ti 70% dng anti v30% dng syn.

0 60 120 300180 240 360Gc quay

E (kcal/mol)

1

2

3


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43

Trong iu kin tng t 1,2-ibrom etan cha 89% dng anti v 11% dngsyn. Nu dng syn ca XCH2-CH2Y c lin kt hidro th s khc thm ch dngsyn bn hn dng anti. Cc cu dng tng i bn ca mt cht l nhng ng

phn cu dng ca nhau.+ Cu dng ca hp cht khng noTrong phn t nhng hp cht loi ny nguyn t hoc nhm nguyn t

mang ni i thng v tr che khut i vi nguyn t H hay cc nhm th nhCl, CH3

C O

O

H

H

C O

O

H

CH3

C O

H2C

H

CH3

Axit fomic Etyl fomiat Metyl vinyl ete

+ Cu dng bn ca mt s phn t c ni ing ch l cc hp cht c 2 ni i lin hp nh: buta-1,3-ien; 1,3-

icrolein c hai dng thng bn ch khc nhau v v tr nhm cha no so vi nin gia. V c s tng t vi ng phn hnh hc nn y ngi ta phn

bit nhng dng l -cis v -trans. i vi butadien-1,3, dng s-trans bn

hn dng s-cis l 2,3 kcal/mol

CH3

CH3

H

H

H

H

CH3

CH3

H

H

H

HDn s nDng anti

C C

CH2 CH2

H H

C C

CH2

HCH2

H

-cis -trans


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44

+ Cu dng ca cc hp cht vng noNhng yu t lm gim bn v bin dng vng no

) Sc cng Baye: (1885) l sc p hoc trng gc ho tr CCC

so vigc ho t bnh thng 109028. Sc cng cng ln th vng cng km bn. Mc sc cng l na hiu s gia gc ho tr ca vng phng v gc ho tr bnhthng, tc l sai lch ca gc ho tr tiu chun.

n (s nguyn t cacbon ca vng) 3 4 5 6 7 ( sai lch v gc) 24 64 9 44 -5 16 -9 33 -12 46

Nh th, theo cc tr s c trng cho sc cng Baye th vng no bn nhtl xiclopentan cn nhng vng no km bn l xiclopropan v nhng vng ln.

Tuy vy, nhng ti liu tch lu cho n nay cho rng kt lun ca Baye chp dng ng cho nhng vng 5 cnh tr xung m thi. Ngi ta tng hpnhng vng ln thy rng: nhng vng ny c bit l xiclohexan c bn lnhn d kin ca Baye nhiu. Xt theo thiu nhit tnh cho mt n v mt xchCH2ca vng trong bng sau:

n H H-157,4 n H H-157,42 168,7 11,3 9 158,8 1,43 166,6 9,2 10 158,6 1,24 164,0 6,5 11 157,4 1

5 158,7 1,3 12 157,7 0,36 157,4 0 13 157,4 07 158,3 0,9 16 157,5 0,18 158,6 1,2 17 157,2 0,2

Ngi ta cng thy nng lng ca cc vng ln t xiclopentan tr ln unh nhau, m theo quan im ca Baye th nng lng phi tng theo s cnh cavng.

) Sc cng Pitz:Thc ra cc vng no (tr xiclopropan) khng phi lvng phng. Trong mt vng, ngoi sc cng Baye cn c sc cng do ch ccnguyn t H trng thi che khut mt phn hay ton phn gy nn. Do , mtvi nguyn t ca vng b lch ra khi mt phng ca vng. Sc cng gi lsc cng Pitze.

Cu dng ca cc vng no) Xiclopropan ch c th trn mt mt phng. Cc nguyn t H trng

thi che khut. Cn cc lin kt C-C b bin dng. Do vng ny t bn.)Xiclobutan ch c th trn mt phng ca 3 nguyn t cn li. iu ny

c xc nh bi cc kt qu nghin cu quang ph cng nh phng php nhiux electron.


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45

1

234

6

5

)Trong xiclopentan hu nh khng c sc cng gc nhng sc y li ln.Do trong trng thi bn ca xiclopentan c mt nguyn t C b chch ra khi

mt phng ca vng 0,5

o

A :

)Cu dng ca xiclohexanHnh dng ca vng xiclohexanXiclohexan cng c cu trc khng phng. m bo cho gc ho tr

bnh thng, xiclohexan cng c nhiu dng khc nhau: dng thuyn, dng xon,dng gh:

Trn cc dng trn, dng gh l dng bn v vy tuyt ai a s cc hpcht c vng xiclohexan cc phn t tn ti hu nh ch dng gh. nhit

phng, trong xiclohexan c ti 99,9% phn t tn ti dng gh.Hai dng ng ch hn c l dng gh v dng thuyn.C 2 dng ny

khng c sc cng Baye v cc gc ho tr ca cacbon u bnh thng (1090

28). dng gh khng c sc cng Pitze nn bn hn dng thuyn.Tht vy, ta c th coi phn t xiclohexan nh t hp ca 6 h thng C-C

ging n-butan. dng gh tt c 6 h thng ny u theo cu dng xen k tngt syn-butan khong cch gia cc nt H 2 nt C k nhau hay khng k nhau uln.

Trong khi , dng thuyn ch c 4 h thng: C1-C2; C3-C4; C4-C5; C6-C1c cu dng xen k cn 2 h thng cn li (C2-C3, C5-C6) c cu dng che khuttng t cu dng che khut ca n-butan. Khng nhng th khong cch cc nt

C2-C4ch cch nhau 1,810

A (so vi tng bn knh VanderWalls 2,40

A ) nn chng

y nhau, kt qu dng thuyn km bn hn dng gh khong 7 kcal/mol.

H

H

H

H

H H

H

H

H

H

H

H

H

H

xiclobutan xiclopentan

HH

H

H

H

H

HH

H

H

H

H

H

HH

H

H

H

H

H

2,490

A

2

3

4

6

xiclopropan


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46

1

2

Cu dng gh ca xiclohexan tn ti gia trng thi cn bng gia 2 dngkhc nhau:

Qu trnh chuyn ho xy ra rt nhanh (106ln/s) phi i qua nhng dngkm bn l dng na gh, dng thuyn v dng xon. Dng xon bn hn dngthuyn khong 1,4 kcal/mol, cn dng na gh km bn nht ( km dng thuyn4 kcal/mol)

Lin kt trc v lin kt bin dng gh 6 nguyn t cacbon c phn b trn hai mt phng song song

v cch nhau 0,50

A ( mi mt phng cha 3 nt cacbon v tr lun phin nhau.Trc i xng bc ba ca nt thng gc vi mt phng . Su lin kt C-C songsong vi trc i xng c gi l lin kt trc, k hiu a; cn su lin kt C-Chng ra ngoi bin ca phn t v to vi trc i xng nhng gc 109 028, gil lin kt bin, k hiu e.

H

CH3 H

H

HCH3 CH3

HH

H

H

CH3

dng gh so snh vi cp syn-butan

H

H

H

HH

H

H

H

H

H

H

H

H

H

H

HH

H

H

H

H

H

H

H

2

3

4

6

Cc lin kt a v e trong xiclohexan (a: axial; e: equatorial)

a

a

a

a

a

a

e

e

e

e

e

e

e

e

e

e

e

e

a

a

a

a

a

a


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47

a e

)Dn xut th ca xiclohexanV c 2 kiu lin kt a v e nn cc dn xut th mt ln ca xiclohexan

c 2 cu dng: dng a v dng e.

Hai dng a v e chuyn ho vi nhau rt nhanh nn khng th tch ringchng vi nhau c, s c mt chng trong cn bng trn c chng minh

bng phng php vt l. Kt qu kho st l thuyt v thc nghim cho thy rngcu to dng e bn hn dng a khong 1,7 kcal/mol. S km bn ca cu dng a sovi dng e do c tng tc syn gia nhm th CH3vi C6, mt khc nhm th CH3tng tc y vi C3v C5(nhm th e khng gy hin tng ny).

CH3

CH3

a

e

CH3

CH3

2

3

4

6

2

3

4

6

Tng tc syn

Tng tc anti


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48

Tng tc syn khng nhng a-metylxiclohexan m cn thy cc dngaxial mt ln th khc na. Tu theo bn cht v kch thc ca nhm th X trong

xiclohexan m s chnh lch v nng lng ca cu dng a v e khc nhau.i vi dn xut th 2 ln ca xiclohexan, 2 nhm th c th v tr 1,1;1,2; 1,3 hoc 1,4. Trong trng hp dn xut th 1,1, nu 2 nhm th ng nht thch c mt dng gh. Nu 2 nhm th khng ng nht s c 2 cu dng gh, trong c mt cu dng u tin l cu dng c nhm th ln v tr e. V d:

Cc cu dng 1,2; 1,3; 1,4 c th tn ti dng cis-trans. ng phn cis-1,2c nhm th phn b theo kiu a,e hoc e,a cn ng phn trans-1,2 hai nhm thl a,a hoc e,e.

Hai cu dng cis-1,2 (a,e) v (e,a) l ng nht nu 2 nhm R l ng nht.Cu dng ny c 3 tng tc syn lm gim bn l: R-C1-C2-R; R-C1-C6-C5;v R-C2-C3-C4. Cu dng trans-1,2 (a,a) c 4 tng tc syn cc h: R-C 1-C2-C3;R-C1-C6-C5; R-C2-C6-C4. Trong khi , cu dng trans-1,2 (e,e) ch c mt tngtc h R-C1-C2-R, v vy cu dng ny bn hn c. nhit phng, trans-1,2-imetylxiclohexan tn ti dng e ti 99%.

CH3

C2H5CH3

F

cis-1,2

trans-1,2

R

RR

R

R

R

1

21

2

1

2

3

3 3

4

4

4

5

55

6 6

6

R

R

R

R

R

R

1

23

4

5 6 1

2

3

4

56

1

2

34

5

6


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49

ng phn cis ca cc dn xut 1,3 hai ln th gm 2 dng a,a v e,e cnng phn trans tn ti di dng a,e v e,a (hai cu dng ny l ng nht vi 2

nhm th l ng nht).

S tng tc syn mi cu dng l cis-1,3 (a,a) l 2; cis-1,3 (e,e) l 0;trans-1,3 (e,a) hoc trans-1,3 (a,e) l 2. V vy, cis-1,3 (e,e) l cu dng bn nht.

Quan h cu dng ca cc dn xut 2 ln th: ng phn trans-1,4 c 2 cudng a,a (4 tng tc syn) v e,e khng c tng tc syn, bn nht; ng phn cis-1,4 c th l a,e hoc e,a (2 tng tc syn).

Trong nhng trng hp c 2 nhm R khng ng nht cc dn xut 1,4cng nh dn xut 2 ln th khc, cc cn bng gia 2 cu dng a,e hoc e,a slch v pha cu dng no c nhm th c kch thc ln v tr e.

Trong nhng dn xut 6 ln th 6 cacbon khc nhau ca xiclohexan

C6H6X6ng ch hn c l hexacloxiclohexxan (X=Cl), hexahidroxylxiclohexan(inozit-X=OH). Nhng dn xut c th c 8 cu dng khc nhau:

RR

13

2

4

5

6 R

R

1

3

2

4

5

6R

R

1

3

2

4

5 6

trans-1,3

R

R 1

32

4

5 6

R

R1

3

2

4

5

6

R

R 13

2

4

5

6

cis-1,3

cis ( )pi allo ( )

muco ( ) neo ( )Sillo ( )

milo ( )

d,l-()

(-)(+)


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50

Trong , c mt cu dng l bin th raxemic d,l. Mi cu dng c k hiuring bng ch ci Hi-Lp (cho C6H6Cl6) hoc ch ci La-tinh (cho inozit

C6H6(OH)6))Cu dng tetrahidropiranTng t xiclohexan, dng gh tetrahiropiran l dng bn. V c d t oxi

nn c 2 dng gh 1C v C1 ( C: chair); chng trng thi cn bng v i xngnhau qua mt phng gng:

Cc hexopiranozo C6H12O6 c 16 ng phn quang hc mi ng phnquang hc mi ng phn c th tn ti dng hay . Mi dng anome nyli c hai dng bn l C1 v 1C. Th d -glucopinarozo gm 2 dng 1C v C1nh sau:

i vi phn ln cc dng pinarozo dng C1 bn hn 1C. C nhiu yu t

lm monosaccarit chuyn t dng ny sang dng khc gi l cc yu t khng bn. l s c mt ca nhm OH axial, nhm CH2OH axial v nhm OH axial cngpha (hiu ng Hatxenotta); nhm OH axial C2 (hiu ng delta 2) nhm OHequatorial C1( hiu ng anome).....

2.3.2. ng ng2.3.2.1. Khi nim

Nhng hp cht c tnh cht vt l v ho hc gn ging nhau nhng khcnhau mt hay nhiu nhm metylen (-CH2-) nm trong mt dy ng ng. Nhng

O O O

C1 1C

O

OH

CH2OH

OH

OH

OH

O

OH

OH

OH

OH

H2COH

C11C


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51

cht nm trong dy gi l cht ng ng. Mt dy ng ng c cng thctng qut chung.

2.3.2.2. Tnh chtCc hp cht trong dy ng ng c tnh cht vt l nh nhit si, nhit

nng chy tng khi tng s nhm metylen, ngha l tng khi lng phn t dotng thm chiu di mch cacbon.

Khi nim ng ng thng dng d on s thay i tnh cht vt lkhi thay i thnh phn nhm metylen.

Cc cht trong dy ng ng cn phi c cng cu trc mch cacbon.

V d:CH3CH2CH2CH3v CH3CH2CH2CH2CH3l hai ng ng ca nhau.(CH3)2CHCH3v (CH3)2CHCH2CH3l hai ng ng ca nhau.CH3CH2CH2CH3 v (CH3)2CHCH2CH3khng phi l ng ng ca nhau

m nm trong hai dy ng ng n - ankan v isoankan.

Hin nay, thng ch ni n dy ng ng ca metan, etylen, axetylen vnhng dy ng ng ca ancol metylic, andehit fomic, axit fomic,...ngha lnhng hp cht c mch cacbon khng nhnh nh n-ankan, n-anken, n-ankin hayn-ancol, n-axit,...

2.3.3. ng cp

2.3.3.1. Khi nimL nhng hp cht c cng s nguyn t cacbon nhng khc nhau mt bi

2n nguyn t hidro.V d:

CH CH, CH2=CH2, CH3-CH3: ng cp

2.3.3.2. Phn loi- Cng v tr lin ktV d:

CH3-CH2-CH2-CH3 , CH2=CH-CH2-CH3, CH C-CH2-CH3

- Khng cng v tr lin ktV d:

CH2=CH-CH2-CH3, CH2-C CH-CH3

2.3.4. Cu hnh2.3.4.1. Khi nim

L mt s qui c t c th bit c cch thc phn b ca ccnguyn t hoc nhm nguyn t ca mt phn t trong khng gian.


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2.3.4.2. Phn loi- Cu hnh hnh hc

- Cu hnh quang hc- Cu hnh cu dng

2.3.4.3. Cu hnh hnh hcGm 3 loi:- Cu hnh cis-trans- Cu hnh syn-anti- Cu hnh E-Z

2.3.4.4. Cu hnh quang hcGm 2 loi:- Cu hnh D-L xt cu hnh D, L phi c nguyn t cacbon bt i v phi biu din

cng thc cu to ca n di dng Fis.Nu nguyn t hoc nhm nguyn t d t ca nguyn t C*nm v pha

bn phi th l cu hnh D v ngc li.V d:

CHO - CH2OH - CH2OH

Trong trng hp nhiu nguyn t C*, xt nguyn t C* no nm gnnguyn t C c s oxi ho thp nht.

V d: HOOC - CHCl - CHOH - CH3

CHO

CH2OH

H OH

Andehit D (+) glixeric

CHO

CH2OH

OH H

Andehit L (-) glixeric

COOH

H Cl

H OH

CH3

HO

Cl H

H

COOH

CH3

COOH

CH3 CH3

COOH

Cl H

H OH

H Cl

HO H

D DL L


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53

- Cu hnh R-S: Do 3 nh bc hc pht minh ra l: Cahn - Ingold -Prelog. Cu hnh R-S c xc nh theo tnh hn cp ca trung tm chiral (C *)theo th t a > b > c > d, ch yu cn c vo s th t (hoc khi lng nguynt) ca cc nguyn t ni vi C*.

V d:Br > Cl > SH > OH > NH2> CH3> HOH > COOH > CHO > CH2OH > CH3

Nu cc nguyn t ni trc tip vi C* l ng nht th cn xt thmnguyn t tip theo, khi y cn ch nhn i hoc ba i vi nguyn t mang nii hoc ni ba.

Biu din cng thc di dng cng thc phi cnh: t t din sao cholin kt vi nguyn t hoc nhm nguyn t tr nht (cp nh nht) i xa phangi quan st th th t phn b ba nhm th cn li s nm trn mt mt phng pha gn ngi quan st s xc nh cu hnh. Nu s gim tnh hn cp ca ccnhm th theo chiu kim ng h th trung tm chiral c cu hnh R (rectus -quay phi), nu theo chiu ngc kim ng h th trung tm c cu hnh S(sinister - quay tri).

c

b

ad

c

da

b

R S

CH2OH

CHO

OH

HOH2C

H

HOCHO

H

ANEHYT R-GLIXERIC ANEHYT S-GLIXERIC

C th hnh dung cc nhm th a, b, c to nn hnh tam gic v nhm d nhnht nm pha sau hnh tam gic :

a

b

c d

R

a

c

b d

S


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54

Cu hnh R-S v Fischer khng c tng quan trc tip.

Trong cc hp cht loi andehit glyxeric c s trng hp cu hnh D -andehit glyxeric l (R)-andehit glyxeric, cn L - andehit glyxeric l (S)-andehitglyxeric.

(D)

C

H

OH

HOH2C CHO

CHOOH

CH2OH

(R)

C

H

OH

HOH2C CHO

OHOHC

CH2OH

(S)

Cu hnh cu dng: (a, e) ch c ngha i vi xiclohexan m thi.

CHO

OH

CH2OH

H

CHO

H

CH2OH

HO

(L)


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55

CU HI V BI TP

Bi 1. Mt HCHC c CTPT C5H12O khi un nng vi axit axetic c mt mtlng nh axit sunfuric lm xc tc cho hp cht c thnh phn C 7H14O2, oxi ha giai on th nht cho xeton thnh phn C5H10O, sau oxi ha mnh tip theos to thnh hn hp axit axetic v axit propionic. Hy suy ra CTCT ca chtC5H12O v vit cc phng trnh phn ng xy ra?Bi 2.Mt HCHC c CTPT C4H8O c kh nng phn ng vi natri bisunfit chohp cht cng bisunfit, tc dng vi hiroxylamin cho oxim, tc dng vi dungdch bc nitrat trong amoniac cho phn ng trng gng v khi oxi ha cho axitisobutyric. Hy suy ra CTCT ca cht C4H8O v vit cc phng trnh phn ngxy ra?

Bi 3.Anken A C6H12c ng phn hnh hc, tc dng vi dd Br2cho hp chtibrom B. B tc dng vi KOH trong ancol un nng cho ien A v 1 ankin C. C

b oxi ho bi KMnO4c, nng cho axit axetic A v CO2. Hy cho bit cu toca ABi 4. Hidrocacbon C7H12 khi oxi ho bng axit cromic to thnh axitxiclopentancacboxylic, khi tc dng vi H2SO4 ri thu phn n chuyn thnhancol C7H14O. Ancol ny cho p iodoform. Xc nh CTCT ca hidrocacbon ?Bi 5. Hp cht A (C7H14O2) phn ng vi (CH3CO)2O to ra B(C7H13O(OCOCH3)). A khng phn ng vi hiroxylamin. Khi ch ha A bngHIO4thu c hp cht C (C7H12O2). C phn ng vi hiroxylamin to ra ioxim.

C kh c dung dch Felinh. 1 mol C phn ng vi 4 mol NaIO to ra ioofomv mui ca axit aipic. Xc nh CTCT ca A v vit phng trnh phn ng?Bi 6.Hp cht A c CTPT C3H7O2N c tnh cht lng tnh. A phn ng viHNO2gii phng kh nit, vi etanol/HCl cho hp cht C5H11O2N. Khi un nngA cho cht c cng thc C6H10O2N2. Xc nh CTCT ca A?Bi 7.Hp cht A (C5H10O3) d tan trong baz long, c tnh quang hot; khi un nhit cao thu c cht B (C5H8O2) khng cn tnh quang hot nhng vncn lm giy qu xanh. S ozon phn cht B cho etanal v axit 2-fomylaxetic.A b oxi ha bng axit cromic cho cht C, cht ny cho 2,4-initrophenylhirazonv phn ng halofom. Vit CTCT ca A, B, C?

Bi 8.Hp cht (A) C5H8O2c th to ioxim, cho p iodoform, p vi bisunfitv cng c kh nng chuyn thnh n-pentan. Xc inh A?Bi 9.Hp cht C7H14O2(A) p vi anhidrit axetic, to thnh C7H13O(OCOCH3)(B) khng phn ng vi phenylhidrazin. Khi ch ho bng Pb(OCOCH3)4, hpcht A chuyn thnh C7H12O2(C)v C p vi NH2OH to thnh C7H12(=N-OH)2,kh c dd Felinh v khi ch ho bng NaOI p vi 4 mol tc nhn to thnhiooform v axit aipic. Gii thch ngn gn cc hin tng quan st thy trn va ra kt lun v cu to ca A?


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Bi 10. Hp cht hu c A ch gm C, H,O. Ho tan 1,03 gam A trong 50 gbenzen ri xc nh nhit si ca dd th thy ts = 80,356oC, trong khi benzen

nguyn cht c nhit si ts = 80,1

o

C. t chy hon ton 21 mg hp cht A ththu c 0,0616 g CO2v 9,0 mg H2O.a, Xc nh CTPT A, bit hng s nghim si trong trng hp ny l 2,61.

b, Bit rng A c th l: hp cht ianehit, ixeton, iphenol, iancol v c khnng cho p iodoform. Vit CT cc ng phn tng ng ni trn?Bi 11.Vit CTCT ca cc HCHC n chc mch h ng vi cc phn t:

a. C4H8O2 b. C5H10O.Bi 12.Nhng cht no sau y c ng phn hnh hc. Biu din cc ng phn v xc nh tn theo danh php ZE?

a. CH3 CH = CH CH3 (A)

b. CH2= CH CH2 CH3 (B)c. CH3 C C CH3 (C)

d. CH3 CH = CH COOH (D)

e. 1,1-imetylxiclopropan (E)f. 1,2-imetylxiclopropan (F)

Bi 13.Nhng cht no sau y c ng phn quang hc. Ti sao? S ng phnquang hc l bao nhiu?CH3CHBrCH3 (A) CH3CHBrCH2CH3 (B)CH3CHBrCHBrCH3 (C) CH3[CH(OH)]4CH=O (D)HOOCCH(OH)CH(OH)COOH (E) HOOC[CH(OH)]3COOH (F)Bi 14.Vit cc cng thc ca cc ng phn lp th (nu c) ca cc cht sau yv cho bit loi ng phn?

a. CH3 CH = CH CH = CH CH3 (A)b. C2H5 CHBr CHBr C2H5 (B)c. CH3 CH = CH CH(CH3) COOH (C)

Bi 15.Vit cu to ca cc hp cht saua) (S)-1-brom-1-clopropan b) (R,R)-1,2- diclobutanc) (S)-bromcloflometan d) (S)-1-deuterietanol) (S)-2-brom-3-deuteri-2-metylpentan e) (R,S)-1,2-butadiolBi 16.Vit tt c cc ng phn lp th ca 1-brom-1,2-diclopropan bng cngthc chiu Fischer v phi cnh. Ch r ng phn threo, erythro, i quang, meso

Bi 17.Vit hai cng thc chiu Newman hay phi cnh ca cu dng xen k calin kt C2-C3 ca 2- methylbutan. So snh bn ca 2 cu dng v so vi

butan trn?Bi 18.Vit hnh chiu Newman hay phi cnh ca 3 cu dng xen k c th cca 2,3-dimetylbutan, trong c 2 cu dng ging nhau, cn 2 cu dng c nnglng khc nhau 0,9 kcal/mol. Cu dng no c nng lng thp nht. Tha nhnHo= Go, Tnh hng s cn bng nhit phng?


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57

Bi 19.Phn tch ng phn lp th ca xyclohexan hai ln th 1,2 vi hai nhmth ging nhau v khc nhau. Gii thch kt qu trn bng cu dng gh ca

xyclohexan?


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58

TI LIU THAM KHO

1. Trn Quc Sn, ng Vn Liu Gio trnh c s ha hc hu c, Tp 1, 2,NXB i hc s phm, 2007.

2. Chu Phm Ngc Sn, Nguyn Hu Tnh,Bi tp ha hc hu c, NXB HnThuyn, Thnh ph H Ch Minh, 1995.

3. Trn Quc Sn, Trn Th Tu, Danh php hp cht hu c, NXB Gio dc,H Ni, 2007.

4. Thi Don Tnh, C ch v phn ng ha hc hu c (tp 1,2,3),NXB Khoahc v k thut, H Ni, 2008.

5. Ng Th ThunHo hc hu c phn bi tp (tp 1,2), NXB Khoa hc v kthut, H Ni, 2006.

6. Hong Trng Ym, Ho hc hu c, NXB Khoa hc & K thut, H Ni,2002.


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CHNG 3: LIN KT TRONG HO HC HU C

Nu trong ho v c ta hay gp lin kt ion (cn gi l lin kt in ho tr)

th trong ho hu c, lin kt cng ho tr l lin kt bao trm v quan trng hnc, sau l lin kt phi tr v lin kt hidro xut hin trong mt s trng hp.

3.1. Lin kt cng ho tr3.1.1. Theo thuyt c in

Thuyt lin kt c in cho rng, khi hai nguyn t kt hp vi nhau, minguyn t gp chung vo mt electron ho tr ca mnh. Cc electron ny chytrn cng mt qu o vi cc electron c to nn lp v kh tr mi nguyn t.V d:

C

H

H

H

H

Quan nim hin i thng nht vi quan nim c in l khi to nn lin kt

cng ho tr, 2 nguyn t gp chung in t, nhng khc v cch gp chung: do sxen ph ca 2 obitan.

3.1.2. Quan nim hin i3.1.2.1. Obitan nguyn t

Theo c hc lng t, cc ht c bn nh electron, proton c bn cht nhnguyn: va c tnh cht ht, va c tnh cht sng.

Schroding thit lp phung trnh tng qut v quan h gia nng lngca electron v hm sng xc nh trng thi ca electron trong nguyn t:

H = E (H l ton t Haminton)

Khi phng trnh tho mn mt s iu kin nht nh th hm s sng l nghim ca phng trnh v c gi l hm sng obitan nguyn t gi tt lobitan nguyn t. Theo nhng kt qu tnh ton, cc obitan ca cc electron ccmc c hnh dng rt khc nhau: obitan s lun lun c dng i xng cu. Ccobitan p c dng hnh s 8 ni. Cc obitan p khc nhau v hng:

y

x

z

x

y

x

y

x

z

S P - Cu trc in t ca nguyn t cacbon v s lai haS phn b 6 in t theo obitan nguyn t cacbon c th biu din nh

sau: 1s22s22px2py2pz. Nh vy, nguyn t C, hai in t lp ngoi (2s2) snh


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i (c spin ngc nhau) v ch c hai in t c thn l 2pxv 2pynn nguynt cacbon c ha tr hai.

Trng hp cacbon c ha tr hai ch gp trong mt s t hp cht nh CO,R-N=C. Cacbon c ha tr 4 hu ht cc hp cht hu c. C hc lng t chorng khi hnh thnh lin kt th cacbon trng thi kch thch: mt in t caobitan 2s nhn mc nng lng cao hn v nhy sang obitan 2p cn trng, do cu hnh in t ca carbon tr thnh: 1s22s12px

12py12pz

1. C th biu din quatrnh kch thch nh sau:

s2

1 p2

2s2

2

s2

1 p3

2s1

2

Nh vy, trng thi kch thch, cacbon c 4 in t khng ghp i: 1in t 2s v 3 in t 2px, 2py, 2pz. S kch thch ny i hi nng lng ln(97kcal/mol). Nng lng d gii phng ra trong s hnh thnh 4 lin kt cacacbon tha b cho nng lng kch thch . V vy, trong phn ln cccht hu c, cacbon c ha tr 4. Cacbon c ha tr 4 khng phi do s dng trctip 4 obitan trn to ra 4 lin kt vi s tham gia ca mt obitan 2s v 3 obitan2px, 2py, 2pz. Nu bn obitan hnh thnh lin kt vi 4 obitan 1s ca bnnguyn t hydro to ra phn t CH4th ngi ta c th ngh rng ba trong bnlin kt C-H phi khc vi lin kt th t (trong 4 lin kt c 1 lin kt to biobitan 1s ca C vi obitan 1s ca H to 1 ng thng, 3 lin kt to bi 3 obitan1s ca H vi orital 2px, 2py, 2pzca C, gc lin kt l 900).

z

y

CH

H

H

H

900

iu ny hon ton mu thun vi thc nghim ca ha hc hu c: bn

lin kt C-H trong phn t CH4 l hon ton ging ht nhau, khng c cch gphn bit chng. gii quyt mu thun ny, Pauling gii thch bng s laiha cc obitan: khi hnh thnh lin kt th obitan 2s v obitan 2p c hin tng laiha vi nhau. Obitan 2s c th lai ha vi ba, hai, mt obitan 2p. C 3 kiu lai hasp3, sp2, sp.


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61

1800

1200109028

sp sp2 sp3

- Lai ha sp3 (lai ha t din) l s t hp 1 obitan s vi 3 obitan p tothnh 4

obitan sp3nh hng theo 4 nh ca mt t din u, gc lai ha 109028.S lai ho sp3c th biu din nh sau:

+

1 3 2s p sp

3

x

y

z s + 3p sp3

lai ha

Cc kt qu tnh ton cho thy rng nu coi kh nng xen ph ca obitans l 1 th obitan p l 3 v obitan lai ho sp3 l 2. Trong phn t mtan cng nhcc ng ng ca n, obitan lai to sp3 ca cacbon xen ph vi obitan 1s cahyro to thnh lin kt (C-H). cc ng ng ca mtan 2 obitan sp3ca hainguyn t cacbon bn cnh nhau to thnh lin kt (C-C). V gc ho tr canguyn t cacbon sp3 l 109028nn mch cacbon trong phn t ankan l ng

gp khc khc hnh ziczc.

H

HH

H

H

H H

H

H

H

H

H

H

H

H H

H

H

H

H

CH CH CH CH CH CH CH4 33 3 2 2 3


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Thc vy cc kt qu tnh ton cho thy rng:+ Obitan lai to tt nht c hng xen ph cao hn obitan s hoc obitan p.

+ 4 obitan lai to tt nht c hng xen ph cao hn hon ton ng nht vinhau.+ Cc obitan ny hng n gc ca mt t din u- tc l s sp xp m

trong cc obitan nm v tr cch xa nhau nht. S lai ho ny gi l lai ho tdin. Gc lai ho trong trng hp ny l 109 028.

- Lai ha sp2l s t hp 1 obitan s vi 2 obitan p to thnh 3 obitansp2 (lai to tam gic hoc lai ho phng). Trc i xng ca 3obitan sp2nm trn mt mt phng to thnh gc 1200. Kh nngxen ph tng i ca obitan sp2l 1,99.

x

y+

+

+

s + 2p sp2

lai ha sp2

s2

1 sp2

p1

2

s2

1 p3

2s1

2

Trong phn t etylen cc obitan sp2tham gia xen ph to nn 5 lin kt c trc nm trong mt mt phng. Cn li 2 obitan p thun khit cha lai to xen

ph bn nhau to thnh lin kt .

H

H

H

H

C C

H

H

H

H

- Lai ha sp: l t hp ca mt obitan s v mt obitan p gp trong ccphn t c ni 3 vi kh nng xen ph l 1,93 v gc to bi trci xng ca 2 obitan l 1800(kiu lai ho ng thng).

-


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+ +- + - +-sp

s + p

Trong phn t axetylen, cc obitan lai ho sp xen ph ln nhau v viobitan hyro (1s) to thnh 3 lin kt m trc lin kt cng nm trn mt ng

thng, cn li 4 obitan p thun khit chng s xen ph bn nhau tng i mt tonn 2 lin kt .

Cc lin kt ca axetylen.

H C C H

3.1.2.2. Obitan phn t lin ktTheo phng php s ho tr cng nh theo phung php MO, lin kt

cng ho tr c hnh thnh do s xen ph cc obtian nguyn t thnh obitanphn t lin kt. Khuynh hng ca s xen ph l tin ti cc i theo nguyn lxen ph cc i. Mun cho cc obitan nguyn t tng tc c hiu lc vi nhauthnh obitan phn t chng phi tho mn 3 iu kin sau y:

1-Nng lng ca chng gn bng nhau.

2- S xen ph mc ln.3- Chng phi c cng mt kiu i xng vi trc ni hai nhn nguyn t.Xt iu kin 3 ta c th xen ph:- Hai obitan s- Mt obitan s vi mt obitan p no c trc i xng trng vi trc ni

hai ht nhn.- Hai obitan p c trc i xng song song vi nhau (cng px, pyhoc pz).

S xen ph c th theo trc hay bn trc ni gia hai ht nhn nguyn t.Theotrc:

s2

1 p3

2s1

2

s2

1 sp p2

2

H H C C CH C H

Lai ha sp


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Obitan lin kt c trc i xng l ng thng ni gia hai ht nhn vc gi l obitan . Lin kt cng ho tr c hnh thnh gi l lin kt . Sxen ph xy ra tng t nh vy i vi trng hp obitan p + p.

S xen ph bn trc:

S xen ph bn trc s to thnh obitan v lin kt .

V obitan khng c tnh i xng i vi trc hai ht nhn m ch ixng vi mt phng nt cha 2 trc nn lin kt t bn, d phn cc ho. Mtkhc cn tr s quay t do ca nguyn t hay nhm nguyn t xung quanh trclin kt (do s quay s vi phm nguyn l cc i). l nguyn nhn lm xuthin cc ng phn hnh hc.

- Lin kt Trong s xen ph theo trc, obitan phn t lin kt c trc i xng l

ung thng ni hai ht nhn, gi l obitan . c im chung ca obitan l c

tnh i xng i vi trc lin kt v cc tiu phn (nguyn t, nhm nguyn t)c th quay tng i t do quanh trc m nng lung tng tc khng thay i.trong ho hu c, ta hay gp 2 kiu xen ph to lin kt sau y:

sp - s sp - sp

+- +-

- + - +

+-+-

*

p p

*

+- +

- + -

+-+

sp

II

+

-

+

-

+

-

-

+

+

-

+

p p

II

II*


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65

c im ca lin kt :+ C s i xng theo trc lin kt.

+ Nng lng lin kt tng i ln (~83 kcal/mol) nn lin kt ny khbn vng.+ Cc nguyn t hay cc nhm nguyn t hai u lin kt c kh nng

quay t do xung quanh trc lin kt m khng lm mt s xen ph (th d H-H,H3C- CH3), do xut hin vn cu dng hp cht hu c.

- Lin kt Khi cc obitan xen ph vi nhau v c 2 pha m trc obitan vn song song

vi nhau gi l s xen ph bn ta c obitan phn t , lin kt c to thnhl lin kt . S xen ph nh vy khng su nn km bn. Hai trc ca 2 obitansong song, nm trong mt phng .

Tuy nhin cc tiu phn khng th t quay quanh trc lin kt v nu quayl ph v xen ph, ph v lin kt.

c im ca lin kt :+ Khng c tnh i xng trc.+ Cc trc obitan p song song nhau to thnh mt phng gi l mt phng

.+ Nng lng lin kt tng i nh (~60 kcal/mol) nn km bn hn

lin kt , n d b phn cc ha hn lin kt .+ Cc nguyn t hay cc nhm nguyn t hai u lin kt khng c kh

nng quay t do nh i vi lin kt v khi quay nh th s vi phm s xen phcc i ca hai AO, ph v lin kt; do c kh nng xut hin ng phn hnhhc cc hp cht c ni i C=C, ni ba CN. . .

3.1.3. c im ca lin kt cng ho tr- Bn v rt bn (kim cng).- Cc lin kt cng ho tr c di xc nh. di lin kt ca cacbon vi ccnguyn t mt phn nhm tng khi s th t tng, vi cc nguyn t ca mt chuk th gim khi s th t tng, sau na l khi ghp tng th di lin kt gim.- Hng khng gian ca cc lin kt l xc nh v lin kt cng ho tr c tnh

bo ho.- Hp cht c lin kt cng ho tr thng to mng tinh th phn t.- phn cc ca lin kt nh, thng < 1,6D.


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- Tan t hoc khng tan trong nc, dung dch dn in km.

3.1.4. Cc lin kt n, i, ba, h lin hp3.1.4.1. Lin kt nTrong cc phn t metan v etan ch c lin kt n, l cc lin kt

kiu sp - s v sp - sp. Nguyn t cacbon trng thi lai ho sp3. Cc lin kt trong phn t metan v etan c m t nh sau:

metan etan

3.1.4.2. Lin kt iTrong phn t etilen, lin kt i C=C gm mt lin kt kiu sp - sp v

mt lin kt . Hai nguyn t cacbon trng thi lai ho sp2. Cc obitan xen ph

to nn nm lin kt . Trc ca nm lin kt ny cng nm trn mt mt phng . Cn li hai obitan p chng s xen ph vi nhau to thnh lin kt . Trc cahai obitan ny song song vi nhau, cng nm trong mt mt phng giao nhau trc lin kt C - C v vung gc vi nhau.

C C

H

H

H

H

3.1.4.3. Lin kt baLin kt ba trong phn t axetilen gm c mt lin kt v hai lin kt .

Hai nguyn t cacbon trng thi lai ho sp. Cc obitan lai ho sp xen ph to nnba lin kt , c trc nm trn mt ng thng. Cn hai obitan pyv pzxen phvi nhau to hai lin kt c mt phng b dc vung gc vi nhau v ct nhau trc lin kt C-C:


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C C HH

3.1.4.4. H lin hpH lin hp l h c nhiu ni i xen k u n vi ni i nh buta-1,3-

ien hay vng benzen.Tng t nh etilen, cc nguyn t cacbon trong cc h u trng thi

lai ho sp2v h cc lin kt l mt h phng. Cc obitan p xen ph vi nhautng i mt to ra hai lin kt nh trong buta-1,3-ien hoc xen ph v c hai

pha to obitan phn t cc lin kt vng kn nh trong benzen:

H

H

HH

H

H

buta-1,3-dien

benzen

3.1.4.5. Tnh thm, phn thm


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- Tnh thmHp cht thm l nhng hp cht vng cha no m tt c nhng nguyn t

mt vng u tham gia to thnh mt h lin hp thng nht, trong cc electron ca h to nn mt vng electron kn. Nhng hp cht thm c nhng c tnhm ngi ta gi l tnh thm.

- Cc iu kin ca tnh thm+ H lin hp hoc p nm trong hp cht vng kn vi s

electron l 4n+2 (bn trng thi c bn): gi l quy tc thm 4n+2 do Huckentm ra t nm 1932. Theo quy tc ny th cc polyen vng vi 4n+2 electron

phi bn vng v c tnh thm.+ Cc lin kt phi nm trn cng mt mt phng (vng thm phi c cu

trc phng). Vng khng nht thit phi ging benzen m c th l vng

cacboxylic khc benzen, d vng hoc vng v c thun tu.+ Nng lng ca hp cht thm thp hn nng lng ca hp cht ccng lin hp mch h.

V d: Hp cht c tnh thm l:

N

benzen piridin naphtalen

Hp cht khng thm l:

O

O

N

N

H

H

H

H

- Tnh phn thm

L nhng hp cht c y 2 yu t (1), (2) nhng c nng lng tn tihoc l bng hoc l ln hn nng lng hp cht mch h c cng lin hp.V d:

xiclo butadien pentalen


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3.2. Lin kt phi tr

Lin kt cng ha tr phi tr (cn c bit n nh l lin kt cng ha trcho nhn) l mt dng c bit ca kt c to thnh, bn ca n khng khcg so vi lin kt cng ha tr.

Cc lin kt cng ha tr phi hp c to thnh khi mt baz Lewis (chtcung cp in t) cung cp mt cp in t cho axit Lewis (cht nhn in t) vhp cht to thnh sau c gi l adduct.

Cc lin kt phi tr c th tm thy trong nhiu cht khc nhau, chng hnnh trong cc phn t n gin nh monoxit cacbon (CO), trong c mt linkt phi tr v hai lin kt cng ha tr thng thng gia nguyn t cacbon vnguyn t oxi, hay trong ion amoni (NH4

+), trong lin kt phi tr c to

thnh gia proton (ion H+

) v nguyn t nit.Cc lin kt phi tr cng c to ra trong cc hp cht thiu in t, chng

hn nh trong clorua berili rn (BeCl2), trong mi nguyn t berili c linkt ti bn nguyn t clo, hai vi lin kt cng ha tr thng thng v hai vi linkt phi tr, iu ny s to cho n mt cp tm (octet) n nh ca cc electron.

Cc lin kt phi tr cng c th tm thy trong cc phc cht phi tr c stham gia ca cc ion kim loi, c bit nu chng l cc ion kim loi chuyn tip.Trong cc phc cht ny, cc cht trong dung dch hot ng nh cc baz Lewisv cung cp cc cp electron t do ca chng cho ion kim loi, trong lt n hotng nh cc axit Lewis v nhn cc electron. Cc lin kt phi tr to ra cc hp

cht gi l phc cht phi tr, trong khi cht cung cp electron c gi l ccphi t.

C rt nhiu cht vi cc nguyn t c cc cp electron c c, chng hnoxi, lu hunh, nit v cc halogen hay cc ion halogenua, m trong dung dch cth cung cp cc cp electron tr thnh cc phi t. Mt phi t thng thngl nc (H2O), n s to thnh cc phc cht phi tr vi bt k ion kim loi ngmnc no. Chng hn Cu2+, to ra [Cu(H2O)6]

2+trong dung dch nc. Cc phit n gin khc l amoniac (NH3), cc ion florua (F

-), clorua (Cl-) v xianua(CN).

Lin kt phi tr l mt loi lin kt cng ho tr m c cp electron lin kt

do mt nguyn t cung cp, nh lin kt N-O hoc S-O trong triankylamin oxitcng nh trong diankyl sunfoxit:

N

R

OR

R

S

R

R

O

Lin kt phi tr cng c th hnh thnh gia hai phn t nh:


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H3N: + B(CH3)3 H3NB(CH3)3

3.3. Cc loi lin kt yu3.3.1. Lin kt hydro3.3.

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