senyawa aromatik.ppt

5/27/2018 Senyawa Aromatik.ppt

1/47


2/47

Cincin benzen

benzen merupakan contoh sederhana senyawa aromatik

fasanya cair, titik didih 80oC

diisolasi pertama kali : 1825 oleh Michael Faraday

strukturnya merupakan teka-teki bagi ahli kimia,R.M : C6H6

memiliki ikatan rangkap tetapi TIDAK menunjukkan

reaktivitas seperti alkena

struktur yang diajukan August Kekule (18291896) :

Hidrokarbon aromatik :

Senyawa siklik karbon dan hidrogen yang memiliki

ikatan tak jenuh.Rumus umum : CnHn

Cincin benzen

benzen merupakan contoh sederhana senyawa aromatik

fasanya cair, titik didih 80oC

diisolasi pertama kali : 1825 oleh Michael Faraday

strukturnya merupakan teka-teki bagi ahli kimia,R.M : C6H6

memiliki ikatan rangkap tetapi TIDAK menunjukkan

reaktivitas seperti alkena

struktur yang diajukan August Kekule (18291896) :

Hidrokarbon aromatik :

Senyawa siklik karbon dan hidrogen yang memiliki

ikatan tak jenuh.Rumus umum : CnHn


3/47

Oleh karena benzen TIDAK

bereaksi seperti alkenamaka ikatan rangkapnya

mempunyai karakter yang

berbeda

Struktur Kekule tidaksepenuhnya tepat !

Struktur baru yang diajukan:

H

H

H

H

H

H

C

CC

C-H

C-H

C

H-

H

H-

-

-

H

O Oatau

delokalisasi elektron


4/47

Penamaan Senyawa Aromatik

1. Menurut aturan IUPAC :

Bila sebuah H diganti oleh atom/gugus lain, diberi namasebagai turunan benzen :

2. Beberapa nama umum yang diadopsi dari sistem IUPAC :

CH2CH3 NO3Br Cl

etilbenzen nitrobenzen bromobenzen klorobenzen

CH3 OH COOH NH2

toluen fenol asam benzoat anilin


5/47

3. Jika terdapat lebih dari 1 substituen, dilakukan penomoran

(jumlahnya serendah mungkin), diurutkan secara alfabet

CH3 CH3 CH3

1-bromo-3-kloro benzen 1,2,4-trimetil benzen 3,5-dikloro toluen

atau 2,4-dimetil toluen

Cl

CH3

CH3

1

3

4

21

Cl

4. Jika hanya 2 substituen, dapat diberi awalan orto-, meta-,

para-Br Br

o-dibromo benzen m-dibromo benzen p-dibromo benzen

Br

Br 1

3

21

Br

Br

1

4


6/47

5. Benzen sebagai substituen fenil :

28

3-fenilpentana difenilmetana

CH3CH2CHCH2CH3

CH2

1 2 3 4 5

CH2 CH3

CH3

fenil benzil p-tolil o-tolil


7/47

Sifat Fisik Hidrokarbon Aromatik

Hidrokarbon alifatik dan alisiklik, benzen danhidrokarbon aromatik lain bersifat nonpolar.

Tak larut dalam air, larut dalam pelarut organik seperti:dietil eter, karbon tetraklorida, atau heksana.

Benzen bersifat toksik dan karsinogenik, sehingga kadangdiganti dengan toluen.

Titik leleh p-substitusi lebih tinggi dari o-dan m-, p-isomerlebih simetris


8/47

Nama Struktur Tl (oC) Td (oC)

Benzen 5,5 80

Toluen -95 111

o-xilen -25 144

m-xilen -48 139

p-xilen 13 138

CH3

CH3

CH3

CH3

CH3

CH3CH3


9/47

Kestabilan cincin benzen

Kalor hidrogenasi:

+ H2Pt

+ 28,6 kkal/mol

sikloheksena sikloheksana

+ 3H2Pt

+ 49,8 kkal/mol

sikloheksanabenzen

225o,

35 atm


10/47

Gambar 10.5


11/47

Ikatan dalam benzen

Rumus Kekule

benzen pada 1865 benzen pada 1872 benzen pada 1940

C

C C

C

CC

H

H

H

H H

H


12/47

Cincin planar dari 6karbon hibridisasi sp2

Masing-masing karbon

mempunyai orbitalpEnam orbitalp tumpang

tindih menghasilkan siklik

sistem


13/47

208 kJ/mol

231 kJ/mol

120 kJ/mol

360 kJ/mol

3 x sikloheksenaStabilitas senyawa aromatik

ditunjukkan oleh DH


14/47

208 kJ/mol

360 kJ/mol

3 x sikloheksena

* panas hidrogenasi= 152 kJ/mol lebihkecil, artinya

benzen lebih stabil*152 kJ/mol = energi

resonansi benzene


15/47

Panas hidrogenasi = 208 kJ/mol

Panas hidrogenasi = 337 kJ/mol

3H2

Pt

3H2

Pt

Konyugasi siklik versus konyugasi nonsiklik


16/47

Requirements for Aromaticity1. Cyclic Compound

2. Planar Compound

3. Fully Conjugated System4. 4n + 2 electrons (Huckels Rule)

Aromaticity; Unusual Stability Associated with

Fully Conjugated Cyclic Systems


17/47

Pyridine

N

O

S

N

H

Pyrrole Furan Thiophene

Heterocyclic Aromatic Compounds

N

Quinoline

N

Isoquinoline


18/47

Reactions of Arenes: A Preview

1. Some reactions involve the ring.a) Electrophilic aromatic substitution

b) b) Nucleophilic aromatic substitution

2. In other reactions the ring is a

substituent.


19/47

Benzylic Hydrogens are Reactive Sites

C H

H

H

Free RadicalHalogenation of Alkyl

Benzenes Oxidation of Alkyl

Benzenes

Nucleophilic

Substitution ofBenzylic Halides


20/47

Free-radical chlorination of toluene

C C

H

H

H

H

H + Cl2

UV

C CH

H

H

H

Cl

+ HCl

CH3

Cl2

light

or

heat

CH2Cl


21/47

Site of Oxidation is Benzylic Carbon

CH3

CH2R

CHR2

or

or

COH

ONa2Cr2O7

H2SO4

H2O

heat

Oxidation of Alkylbenzenes

O


22/47

Na2Cr2O7

H2SO

4

H2O

heat

COH

O

CH3

NO2 NO2

Na2Cr2O7

H2SO4

H2O

heat

CH(CH3)2

CH3

COH

O

COH

O


23/47

Reactions of Arenes:Electrophilic Aromatic Substitution

H E

+ E Y + H Y

+

part 1


24/47

Aromatic Compounds React Differently

Than Alkenes

+ Cl2

Cl

Cl

+ Cl2

FeCl3Cl

Addition

Substitution


25/47

Electrophilic Aromatic Substitution Reaction

X2,FeX3

(X = Cl, Br)

X

HONO2

H2SO4

NO2

SO3

H2SO4

SO3H

RCl, AlCl3

(R can rearrange)

R

R C

O

Cl, AlCl3 C

O

R

Halogenation

Nitration

Sulfonation

Friedel- Crafts Alkilation

Friedel-Crafts Acylation


26/47

Step 1: attack of electrophile

on -electron system of aromatic ring

highly endothermic

carbocation is allylic, but not aromatic

H H

H H

H H

E+

H H

H

H

H H E

+

Electrophilic Aromatic Substitution Mechanism


27/47

Step 2: loss of a proton from the carbocationintermediate

highly exothermic

this step restores aromaticity of ring

HH

H

H

HHE

+

HH

HE

HH

H+

Electrophilic Aromatic Substitution Mechanism


28/47

H

Nitration of Benzene

+ + H2O

H2SO4

HONO2

NO2

Electrophile is

nitronium ionO N O

+

NET REACTION


29/47

Step 1a; Formation of Strong Electrophile

H O N

O

O

+ H+ H O N

O

O

H

+

H O N

O

O

H

+

H2O

-

+ O N O

+


30/47

Step 1b: attack of nitronium cation

on -electron system of aromatic ring

H H

H H

H HNO2+

H H

H

H

H H NO2

+

H H

H

H

H H NO2

+

H H

H NO2

H H

H+

Step 2: Water molecule will abstract a proton

from the carbocation intermediate


31/47

H

Sulfonation of Benzene

+ + H2O

heat

HOSO2OH

SO2OH

Several electrophiles present:

a major one is sulfur trioxide

OS

O

O

+


32/47

Halogenation of Benzene

H

++ HBr

FeBr3

Br2

Br

Electrophile is a Lewis acid-Lewis base

complex between FeBr3and Br2.

NET REACTION

+

Br Br

Lewis base Lewis acid

FeBr3 Br Br

FeBr3

+

Complex


33/47

H

Friedel-Crafts Alkylation of Benzene

+ + HCl

AlCl3 C(CH3)3

(CH3)3CCl

Electrophile is

tert-butyl cation C CH3

H3C

H3C

+


34/47

Role of AlCl3

acts as a Lewis acid to promote ionizationof the alkyl halide

(CH3)3C Cl

+ AlCl3

+

(CH3)3C Cl

AlCl3

(CH3)3C

+

Cl

AlCl3

+


35/47

Rearrangements in Friedel-Crafts Alkylation

Carbocations are intermediates.

Therefore, rearrangements can occur

H

(CH3)2CHCH2Cl

AlCl3

Isobutyl chloride tert-Butylbenzene

(66%)

C(CH3)3

+


36/47

H

Friedel-Crafts Acylation of Benzene

++ HCl

AlCl3

O

CH3CH2CCl

CCH2CH3

O

Electrophile is an acyl cation

CH3CH2C O

+

CH3CH2C O

+


37/47

Acylation-Reduction

H

O

CR

AlCl3

RCCl

O

Zn(Hg), HCl

CH2R

permits primary alkyl groups to be attached

to an aromatic ring

H2NNH2, KOH,

triethylene glycol,

heatOR

E l P i b lb


38/47

Example: Prepare isobutylbenzene

No! Friedel-Crafts alkylation of benzene using isobutylchloride fails because of carbocation rearrangement.

(CH3)2CHCH2Cl

AlCl3

CH2CH(CH3)3

isobutylbenzene

C(CH3)3

Actual Product


39/47

Use Acylation-Reduction Instead

+ (CH3)2CHCCl

O

AlCl3

O

CCH(CH3)2

Zn(Hg)

HCl

CH2CH(CH3)3


40/47

Lokasi penempatan substituen ke-

dua ditentukan oleh substituen

pertama -> apakah pada posisiorto, meta atau para.


41/47

Summary of Substituen Effects on Orientation

o- and p-director

H2N RHN R2N

HO

RO

HNRC

O

R

X

m-director

RC

O

RO2C

HO3S

HC

O

HO2C

CN

O2N

+R3N

stronglyactivating

stronglydeactivating


42/47

Multiple Subsistent Effects

1. If both constituents direct to the same spot;

then that location is major site of substitution.

CH3

NO2

CH3

NO2

Br

86-90%

Br2

FeBr3


43/47

Multiple Subsistent Effects

CH3

CH3

O

AlCl3

O

CH3CCl+

CH3

CH3

CCH3

99%


44/47

NHCH3

Cl

Br2

87%

FeBr3

NHCH3

Cl

Br

strongly

activating

2. If the 2 groups direct to different positions;

regioselectivity is controlled by the

most activating substituent


45/47

If the 2 groups direct to different sites;

and activating effects are similar...

3. Substitution occurs ortho to the smaller group

CH3

C(CH3)3

CH3

C(CH3)3

NO2HNO3

H2SO4

88%


46/47

Steric effects control regioselectivity when

electronic effects are similar

4. Position between two substituents is lastposition to be substituted

CH3

CH3

HNO3

H2SO4

98%

NO2

CH3

CH3


47/47

senyawa aromatik.ppt

Documents