MT S VN V SACCARIT TRONG GING DY

MT S VN V SACCARIT TRONG GING DY

CC LP CHUYN HA HC PH THNG

Th.s. Cao vn Giang.

Trng THPTchuyn HSP H ni

LI NI U

Trong qu trnh ging dy cho cc lp chuyn Ha hc phn cacbohydrat, chng ti nhn thy rng: hc sinh rt lng tng trong phn cu trc phn t, cc danh php tng i v tuyt i, vn dng gii cc bi tp. Nhm trao i tho g bt cc lng tng , chng ti ly monosaccarit lm c s cho vic nghin cu saccarit. Trong phm vi bi vit ny chng ti ch trnh by cc vn sau:

1.Mt s khi nim m u.

2. Phn loi.

3. Cu trc ca monosaccarit

4.Cc phn ng tiu biu

5. Gii thiu mt s bi tp c tuyn ch t thi hc sinh gii mn Ha hc cp quc gia, quc t.

CACBOHIRAT.

I. MT S KHI NIM M U.

Cacbohidrat l nhm hp cht hu c tp chc , c nhiu trong thin nhin, c bit trong thc vt (chim trn 80% khi lng kh)

I.1. Cc tn gi khc nhau ca cacbohydrat

1. Cacbohidrat

Cng thc phn t ca chng c dng Cn(H2O)m , nn c gi l cacbohidrat. Tuy nhin chng khng phi l hiddrat ca cacbon. Cacbon khng tan trong nc..2. ng ng ( sugar). T sugar c xut x t ting Phn. su ngha l ngt gar ngha l ct., tc l ct ngt.

3. Saccarit

Ting Latinh saccharum cng c ngha l ng v t t saccarit c dng thay cho t cacbohidrat.

4. Gluxit

Tn ny c xut x t ting Hi-lp glucus) ngha l ngt.

Tm li cacbohidrat, ng, saccarit l ba tn gi khc nhau ca cng mt loi hp cht hu c.

I.2. Phn loi:

Cacbohirat c phn thnh ba nhm chnh sau y:

1. Monosaccarit (monoz): l nhm cacbohirat n gin nht, khng th thy phn c. V d: glucoz, fructoz (C6H12O6) .

Monosaccarit dng mch h nu thuc loi polihidroxiandehyd th gi l andoz, cn nu thuc loi polihidroxixeton th gi l xetoz. Chng u c ui oz ( ting Anh ose)

Ty vo s nguyn t cacbon trong phn t m monosaccarits c gi l :

3C- Trioz ( andotrioz hoc xetotrioz)

4C- tetroz, 5C- pentoz, 6C- hexoz, 7C- heptoz

2. Oligosaccarit (oligoz): l nhm cacbohirat m khi thy phn hon ton sinh ra 2 - 10 phn t monosaccarit. V d: saccaroz, mantoz (C12H22O11) , rafinoz,melexitoz (C18H32O16)

3. Polisaccarit: l nhm cacbohirat phc tp m khi thy phn n cng sinh ra nhiu hn 10 phn t monosaccarit. V d: tinh bt, xenluloz (C6H10O5)n

Polisaccarit c chia thnh 2 loi: homopolisaccarit v heteropolisaccarit.

homopolisaccarit khi b thy phn hon ton cho nhiu hn 10 monosaccarit cng loi v d tinh bt, xenluloz.

Heteropolisaccarit khi b thy phn n cng cho 2 hay nhiu loi monosaccarit khc nhau v d aga-aga.

II- CU TRC PHN T.

Cn phi ni r hn v khi nim cu trc phn t, n bao gm cu to phn t v hnh dng khng gian ca phn t thng hiu l cu hnh phn t

1. Cu to dng mch h ca monosaccarit.Cu to dng mch h ca monosaccarit v d ca glucozo c xc nh bng thc nghim. C th tm tt bng s cc phn ng sau

T cc th nghim suy ra :

(1) glucozo c chc andehyd CHO

(2) glucozo c 5 nhm OH , thuc ru 5 chc

(3) v (4) suy ra gluco c mch cacbon khng phn nhnh. Vy cu to dng mch h ca glucoz nh sau

Vit gn l CH2(OH)(CHOH)4CHO

2. Cu hnh ca monosaccarit. ng phn quang hc

a. Cu hnh ca andohexoz

Ta ly polihidroxiandehyd n gin nht l glixerandehyd hay 2,3-dihidroxipropanal lm v d in hnh kho st. Phn t n c mt nguyn t cacbon bt i (C*) hay cn gi l c 1 trung tm bt i nn c 2 enantiome hay hai i quang

Cu hnh S : OH > CHO >CH2OH > H

Anohexoz c 4C* ( 4 nguyn t cacbon bt i s c 24 = 16 ng phn gm c 8 ng phn dy D v 8 ng phn dy L. Tuy nhin trong t nhin ch gp cc ng phn dy D.

V d

Ch !

*Cc andohexoz ch khc nhau cu hnh ca mt nguyn t C* c gi l ng phn epime ca nhau th d cc cp ng phn epime C2 l D- glucoz v D- mantoz; C4 l D-glucoz v D-galactoz.

* cu hnh tng i l cu hnh dng glixerandehyd lm chun gn vi danh php D/L. Cu hnh tuyt i l cu hnh gn vi trung tm bt i v gn vi danh php R/S.

b.Cu hnh ca xetohexoz

Tng t nh andoz, xetoz ly 1,3,4-trihidroxibutan-2-on-lm chun cho danh php D/L

D-eritruloz lm chun cho dy D

Cc xetohexoz c cng thc cu to

Phn t c 3 nguyn t C* nn co 23 = 8 ng phn quang hc. 4 dy D v 4 dy L.

4 ng phn dy D ca xetohexozo

Trong thin nhin Arabinoz tn ti ch yu dng L(+)-arabinoz.

3. Cu trc mch vng ca monosaccarit-ng phn anome.

a.Cu hnh

trng thi rn, cc monosaccarit tn ti ch yu dng mch vng 5, cnh hoc 6 cnh. Nh bit phn xicloancan, vng 6 cnh l ch yu.Vng 5 cnh gi l furanoz , 6 cnh gi l pyranoz. V d i vi D- glucoz l

Dng vng c to ra do nguyn t H ca nhm OH C5 tch ra cng vo nhm cacbonyl C=O C1 to ra nhm C1-OH, nhm OH ny c gi l nhm hidroxyl semiaxetal (hay hemiaxetal). ng phn c nhm hemiaxetal nm bn phi gi l ng phn , cn nm bn tri gi l. Hai ng phn ny ch khc nhau cu hnh C1( nguyn t C* mi hnh thnh) c gi l hai ng phn anome.

Ty tng monosaccarit m hm lng tng ng phn anome trong cn bng cng khc nhau. ng phn anome no c nng lng nh hn s chim hm lng cao hn.

V d: i vi glucoz v galactoz, t l : l 3 6 : 64, trong khi i vi manoz t l ny l 68:32.

Dng vng ca monosaccarit c biu din dng chiu Haworth ( c l Havooc). Vng 5,6 cnh c qui c chiu xung mt phng thng gc vi mt phng trang giy. Nguyn t O trong vng c vit nh bn phi xa mt ta. Trong dung dch nc cc andohexoz tn ti ng thi c dng mch h v c hai loi vng 5 cnh 6 cnh, cc dng ny chuyn ha cho nhau theo mt cn bng.

Cng thc chiu Haworth ca cc dng andohexoz

Ch ! Trn c s cu trc vng c th gii thch mt s hin tng sau:

Hin tng 1:Ha tan ng phn -(D)-glucoz tinh khit c gc quay cc ring vo nc; hoc ha tan

EMBED Equation.DSMT4 -(D)-glucoz tinh khit c gc quay cc ring vo nc. Khi t ti cn bng u thu c dung dch c . Hin tng ny xy ra l do s chuyn ha gia hai ng phn anome trong dung dch cn gi l s quay h bin. Ta c th tm c % s mol mi ng phn trng thi cn bng nh sau:

Gi s mol v ln lt l x, y. ta c h x+y=1 v 112x + 18,7y=52,7. T tm c x= 0,36, y-0,64.

Hin tng 2: Cho hoc -(D)-glucoz pyranoz tc dng vi CH3OH c mt ca kh HCl khan xc tc, thy ch c 1 nhm OH phn ng, l nhm semiaxetal tm thnh metylglucozit

Khi nhm OH C1 chuyn thnh nhm OCH3, dng vng khng th chuyn sang dng mch h c na.

Phn ng ny dng chng minh dng mch vng ca glucoz

b.Cu dng Tng t nh xiclohexan cac hexopiranoz tn ti dng gh: dng C1 v 1C. V d:

-(D)-glucozpyranoz -(D)-glucozpyranoz

Cu trc vng ca xetohexoz cng c xem xt tng t nh andohexoz

III. MT S PHN NG TIU BIU

III.1. Phn ng ca nhm hydroxyl

a. Phn ng vi Cu(OH)2, trong mi trng kim to thnh phc cht mu xanh lam ging poliancol.

b. Phn ng to este. Ging ancol, cc monosaccarit tc dung vi clorua axit hoc anhydrit axit, s to thnh este

c. Phn ng to glicozit

Do nh hng ca nguyn t oxy trong vng m nh -OH semiaxetal c kh nng phn ng cao hn cc nhm OH khc v d to metyglicozit.

d. Phn ng to thnh ete

e. Phn ng to axetal vng v xetal vng.

III.2. Phn ng ca nhm cacbonyl.

a. Phn ng oxy ha gi nguyn mch cacbon.

Nhm chc an dehyd ca monosaccarit b oxi ha bi ion Ag+ trong dung dch amoniac, (thuc th Tollens), ion Cu2+ trong mi trng kim hoc thuc th Fehling, nc brom vvto thnh axit andonic hoc mui ca chng.

CH2OH[CHOH]4CHO + 2[Ag(NH3)2]OHCH2OH[CHOH]4COONH4 + 2Ag + 3NH3 + H2O (amoni gluconat)

- Vi dung dch Cu(OH)2 trong NaOH, un nng (thuc th Felinh)

CH2OH[CHOH]4CHO + 2Cu(OH)2 + NaOHCH2OH[CHOH]4COONa + Cu2O + 2H2O (natri gluconat)

( gch)

- Vi dung dch nc brom:

CH2OH[CHOH]4CHO + Br2 + H2O CH2OH[CHOH]4COOH + 2HBr

Khi oxi ha bng dung dch HNO3 long c nhm CHO ln nhm CH2OH cui mch cng b oxi ha thnh axit anddaarric hoc saccaric. V d

b.Phn ng oxy ha ct mch cacbon

b. phn ng kh.

c. Phn ng tng mch cacbon

Theo phng php ca Kiliani-Fischer, cho monosaccarit tc dung vi HCN, ri qua mt chui phn ng s thu c monosaccarit tng thm 1 nguyn t cacbon

d. Phn ng ct ngn mch cacbon

d.1. Phng php thoi phn ca Ruff

Phng php ny cho hiu sut thp.

d.2. Phng php Wohl

6.Ph e. Phn ng to ozazon

III.3. Phn ng ln men .

Nh tc dng xc tc ca cc enzim khc nhau, monosaccarit c th to ra nhiu sn phm khc nhau.

V d: Glucoz ln men nh sau

1. ln men ru.

2. ln men lactic

axit lac tic

3. ln men butyric

axit butyric

4. ln men xitric

axit xitric

VI.MT S BI TP TUYN CHN V SACCARIT.Bi 1 ( cu 4.2 thi chon HSGQG-2011)

Hng dn gii

Bi 2 ( QG 2010 cu 10.2 v 10.3)

10.2. Inulin (mt cacbohirat c trong r cy actis) khng phn ng vi thuc th Felinh; khi b thu phn c mt -glucoziaza cho 2 mol glucoz v mt polisaccarit gm cc D-fructoz kt cu theo kiu (21)-D-fructofuranoz. Phn t khi tng i ca inulin khong 5200 u.

V cng thc Havooc (Haworth) ca inulin.

10.3. Phng php bo v nhm hiroxyl (-OH) thng c s dng khi chuyn ho gia cc monosaccarit.

Vit s phn ng iu ch -D-perosinamid t v cc cht cn thit.

Hng dn gii

10.2. Cng thc ca Inulin:

(Hoc v 2 gc glucoz cng mt u)

10.3.

Bi 3 (Cu V.1 v cu V.2 thi chn TQG d thi IChO-2009).

Cho s chuyn ho sau:

a) Vit cng thc cu trc ca A (c biu din cu hnh ca tng nguyn t cacbon bt i). A thuc dy no (D hay L) v dng -glicozit hay

b) Vit cng thc cu to ca B v C bit rng B khng cha nhm cacbonyl. Gii thch s to thnh B.

c) V sao B khng cha nhm cacbonyl m vn b kh bi hiro?

Hng dn gii:

a) Cu trc ca A l

N thuc dy L, loi -glicozit.

b) Sau khi phn ng vi HIO4, mt nhm anehit b hirat ho thnh gem iol, cht ny to vng vi nhm anehit th hai, tip theo l phn ng metyl ho.

c) Di tc dng ca nhit, B m vng, b ehirat ho tr li anehit v do b kh.

Bi 4 ( cu V.2 thi chn TQG d thi IchO-2008)

V.2. Vit s phn ng oxi ha D-glucoz to thnh axit anonic v axit anaric, cng thc Haworth cc mono v i -lacton ca chng v gi tn cc lacton y.

Hng dn gii

Cc sn phm oxi ho D-glucoz v cc lacton ca n

Bi 5 ( Cu 21 bi tp chun b cho IchO-41)

Cc xetoz l mt nhm c bit trong cc ng. Cc dn xut ca D-ribuloz ng mt vai tr quan trng trong tng hp quang ha. Mt -metyl glycosit ca D-ribuloz (A) c th c iu ch t D-ribuloz bng cc x l vi metanol v xc tc axit. un nng A trong axeton c mt HCl dn n s to thnh B l mt dn xut ca propyliden. Axeton to thnh axetal vi cc vic-diol nu hai nhm OH c nh hng khng gian thch hp.

a) Trong qu trnh tng hp B th c th to thnh hai cu trc. V cu trc ca chng v cho bit u l sn phm chnh.

B phn ng vi anhydrit axetic (c mt xc tc) to thnh C. D c to thnh C bng cch un nng trong axit long. D phn ng vi metanol c mt axit to thnh E.

b) V cu trc ca cc cht t C-E.

c) Liu c th xc nh c cu dng ca nguyn t cacbon C1 trong E?

Mc d s to thnh cc axetonit l mt phng php gi tr bo v nhm OH quan trng nhng trong nhiu trng hp n cho nhiu sn phm (hay thnh phn sn phm ph thuc nhiu vo iu kin phn ng). Ni chung y l trng hp hay gp i vi cc ng c cu trc vng 6 cnh.

Ngi ta chng minh rng khng h c s to thnh axetonit khi hai nhm OH k nhau chim v tr axial. Tuy nhin cc vic-diol c nhm OH chim hai v tr equatorial hay mt axial mt equaorial u phn ng c vi axeton/HCl.

d) V hai cu dng gh ca 1-O-metyl-6-O-acetyl--D-galactoz (F). nh du cc nhm OH v tr axial (a) hay equatorial (e). Xc nh cu dng bn nht.

e) C bao nhiu ng phn axetonit c th c to thnh t hp cht ny v c bao nhiu cu dng gh khc nhau ca cc axetonit ny tn ti c?

f) V cng thc chiu Haworth ca L-galactoz

Hng dn gii

a)

S to thnh ng phn 1,3 t ph hp hn (do cc nhm th vi tr trans khng thun li cho vic to vng) nn sn phm chnh s l 3,4-acetonide

b)

c) Khng, v D c nhm OH cha b kha cho nn trong qu trnh tng hp E th c th to thnh c c hai ng phn ( v (. Thnh phn cc ng phn ny ph thuc nhiu vo iu kin phn ng:

d)

e)

Nh vy ng phn 3,4-axetonide c hai cu dng gh khc nhau cn ng phn 2,3 ch mt:

f)

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