CHAPTER 6-AROMATIC COMPOUND.ppt

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6.1INTRODUCTION

2

- In earlier time, compounds are calledaromatic because of their pleasantodours.

- Today, we use the word aromatic torefer to benzene and its structuralrelatives (benzene ring).

- romatic compound is a cyclic

con!ugated molecule or ion that isstabilized by π electron delocalization.

- It is characterized by substitution

reactions.



- "e#ule was the $rst to formulate a

reasonable representation of benzene.- The #e#ule structure suggests alternatingdouble and single carbon-carbon bonds

6.1.16.1.1 KEKULE’S STRUCTUREKEKULE’S STRUCTURE

%

&

&

&&

&

&

'

'

'

'

'

'

o

r



- enzene is actually a resonance hybrid of the two

"e#ule structure.- The bond angles of the carbon atoms in thebenzene ring are 2*°.-

6.1.26.1.2 RESONANCE STRUCTURERESONANCE STRUCTURE

+

uivalent to

-ll &-& bond length eual %/ pm

-0horter than typical &-& (+1 pm)

-onger than typical && (%+ pm)



enzene as the parent name 3 thesubstituent is indicated by a pre$4.

6.26.2 IUPAC NOMENCLATUREIUPAC NOMENCLATURE

((benzenebenzene))

Mono-substituted BenzeneMono-substituted Benzene

5

6 &l r

782 7'2

&'2

&'%

6lourobenzene &hlorobenzene romobenzene

7itrobenzene minobenzene thylbenzene



The enzene ring and the substituentcombine to form a parent name or others.

9

&'% 8' &88'

&'8 7'208%'

Toluene :methylbenzene

;henol :hydro4ybenzene

enzoic acid

enzaldehyde niline :aminobenzene

enzenesulphonic acid

&8&'%

cetophenon

782

7itrobenzene



<hen 2 same substituent are present, theirposition is indicated by pre$4es ortho, meta and para (o-, m- and p- ) or by the use ofnumbers.

Di-substituted Benzene (2 sameDi-substituted Benzene (2 same

substituent)substituent)

=

,2-dibromobenzene

oro- dibromobenzene

,%-dibromobenzene

orm- dibromobenzene

,+-dibromobenzene

or p- dibromobenzene

r

r

2

r

r

2

%

r

r

2

%

+

o-: substituent at

a!b"n 1#2

m-: substituent

at a!b"n 1#$

p-: substituent

at a!b"n 1#%



<hen 2 di>erent substituent are present,select one of the substituent that give newparent name and numbered as &.

Di-substituted Benzene (2 diferentDi-substituted Benzene (2 diferent

substituent)substituent)

1

2-nitrobenzoic acid

oro-nitrobenzoic acid

%-nitrobenzoic acid

orm-nitrobenzoic acid

+-nitrobenzoic acid

or p-nitrobenzoic acid

&88'

782

2

&88'

782

2

%

&88'

782

2

%

+

Pa!ent na&e' ben"i ai

o-: substituent at C 2* m-: substituent at C $*

p-: substituent C %



;osition of substituent must be indicated bynumbers.

The substituent are listed alphabeticallywhen writing the name.

Three or more Substituted BenzeneThree or more Substituted Benzene

/

,2,+-tribromobenzene

r

r

2

%

+r

r

I

2

%

&l

2-bromo--chloro-%-iodobenzene



& atom bearing the substituent that de$nethe new parent name is numbered as & .

*

2,+-dinitrophenol

8'

782

2

%

+

782

%,5-dihydro4ybenzoicacid

9

5'8 8'

2

%

+

&88'

r r

2%

+

7'2

2,+-dibromoaniline

r &'%

2%

+

&'%

+-bromo-2-methyltoluene :+-bromo-,2-dimethylbenzene



Example: Exam ple:

11



enzene ring as substituent. If al#yl substituent is larger than the ring

(more than 9 &) the compound is named asphenyl-substituted al#ane.

;henyl &9'5? ;h

Phenyl GroupPhenyl Group

2

2-phenylheptane

&'2

&'-&'2-&'2-&'2-&'2-&'%

2 % + 5 9 =



If the chain is unsaturated (have && or&≡&) or contains important functionalgroup, the benzene ring is considered asphenyl substituent.

%

-phenyl-2-butene

&'2-&'&'-

&'%

2 % +

2-phenylethanol

&'2-&'2-8'2



Benzyl GroupBenzyl Group

+

phenyl group

&'2− C+2r

benzyl group benzyl bromide :bromomethyl benzyl

C+28

'

benzyl alcohol



6.%6.% C+EMICAL REACTIONS O,C+EMICAL REACTIONS O,

-ENENE-ENENE

8@IATI87 B&TI87

AAITI87 B&TI87

6B BAI& &TB8;'II& 0C0TITCTI87

+ALO/ENATION

NITRATION

,RIEDAL0CRA,T ALKLATION

,RIEDAL0CRA,T ACLATION 5

6 % 16 % 1 ELECTROP+ILICELECTROP+ILIC



- Dost characteristic reaction of benzene.

- H atom is replaced by an electrophile.

6.%.16.%.1 ELECTROP+ILICELECTROP+ILIC

SU-STITUTIONSU-STITUTION

9

'E E

electrophile

E'E



=

@2, 6e@%

@ &l, r

@

782

B

8

&−B

'78%

'208+

B&l, l&l%

(B canrearrange)

B&*&l, l&l%

E '@

E '28

E '&l

E '&l

.

+ALO/ENATIO

N

NITRATION

,RIEDEL0

CRA,TSALKLATION

,RIEDEL0

CRA,TS

ACLATION

'2

7i

+IDRO/ENATION



Reatants' benzene and halogens (&l2 or

r2).

C"niti"ns' ewis acid such as 6e&l% or

6er%

6.%.1.16.%.1.1 +ALO/ENATION+ALO/ENATION

1

E r2

7o reaction

(decolorization notobserved)

E r2

r

E'r

bromobenzen

e

6er%



Reatants' benzene and concentration

'78%.

C"niti"ns' concentration '208+

6.%.1.26.%.1.2 NITRATIONNITRATION

/

'78%782

E 'E

nitrobenzene

E'208+

E

'08+-



Reatants' benzene and haloal#ane.

C"niti"ns' ewis acid such as l&l% or lr%

6.%.1.$6.%.1.$ ,RIEDEL0CRA,T ALKLATION,RIEDEL0CRA,T ALKLATION

2*

l&l%

B

E'&l

al#ylbenzene

E B-@

l&l%E'&l

al#ylbenzene

E

2-chloropropan

e

&l&'%&'&'%

-

&'(&'%

)

2



Reatants' benzene and acid chloride.

C"niti"ns' ewis acid such as l&l% or lr%

P!"ut' #etone

6.%.1.%6.%.1.% ,RIEDEL0CRA,T ACLATION,RIEDEL0CRA,T ACLATION

2

l&l%E'&l

acetophenon

e

E

acetylchloride

8 &'%&-&l

.

8

&&'%

.

8

B&− .

acyl

group

8

&'%&− .

acetyl group

8

− &− .

benzoylrou

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CHAPTER 6-AROMATIC COMPOUND.ppt