12 12 substituent effects in electrophilic aromatic substitution activating substituents
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12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents. Table 12.2. Classification of Substituents in Electrophilic Aromatic Substitution Reactions. Very strongly activating Strongly activating Activating Standard of comparison is H Deactivating

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12 12 substituent effects in electrophilic aromatic substitution activating substituents l.jpg
12.12Substituent Effects in ElectrophilicAromatic Substitution:Activating Substituents


Table 12 2 l.jpg
Table 12.2

  • Classification of Substituents in Electrophilic Aromatic Substitution Reactions

Very strongly activating

Strongly activating

Activating

Standard of comparison is H

Deactivating

Strongly deactivating

Very strongly deactivating


Generalizations l.jpg
Generalizations

1. All activating substituents are ortho-para directors.

2. Halogen substituents are slightly deactivating but ortho-para directing.

3. Strongly deactivating substituents are meta directors.


Electron releasing groups ergs l.jpg
Electron-Releasing Groups (ERGs)

are ortho-para directing and activating

ERG

ERGs include —R, —Ar, and —C=C


Electron releasing groups ergs5 l.jpg
Electron-Releasing Groups (ERGs)

are ortho-para directing and strongly activating

ERG

ERGs such as —OH, and —OR arestrongly activating


Nitration of phenol l.jpg

OH

OH

OH

NO2

NO2

Nitration of Phenol

occurs about 1000 times faster than nitration of benzene

HNO3

+

44%

56%


Bromination of anisole l.jpg

OCH3

OCH3

Br

Bromination of Anisole

FeBr3 catalyst not necessary

Br2

aceticacid

90%


Oxygen lone pair stabilizes intermediate l.jpg

••

••

+

OCH3

OCH3

OCH3

H

H

H

H

+

+

H

H

H

H

Br

Br

H

H

Oxygen Lone Pair Stabilizes Intermediate

••

all atomshave octets

H

H

H

H

Br

H


Electron releasing groups ergs9 l.jpg

Electron-Releasing Groups (ERGs)

ERG

ERGs with a lone pair on the atom directlyattached to the ring are ortho-para directingand strongly activating


Examples l.jpg

O

••

••

••

ERG =

OH

OR

OCR

O

NH2

NHR

NR2

NHCR

Examples

All of these are ortho-para directingand strongly to very strongly activating


Lone pair stabilizes intermediates for ortho and para substitution l.jpg

+

+

ERG

ERG

H

H

H

H

X

H

H

H

H

X

H

H

Lone Pair Stabilizes Intermediates forortho and para Substitution

comparable stabilization not possible for intermediate leading to meta substitution


12 13 substituent effects in electrophilic aromatic substitution strongly deactivating substituents l.jpg
12.13Substituent Effects in ElectrophilicAromatic Substitution:Strongly Deactivating Substituents


Ergs stabilize intermediates for ortho and para substitution l.jpg

ERG

ERG

X

H

H

H

+

+

H

H

H

H

H

X

H

H

ERGs Stabilize Intermediates forortho and para Substitution


Electron withdrawing groups ewgs destabilize intermediates for ortho and para substitution l.jpg
Electron-withdrawing Groups (EWGs) DestabilizeIntermediates for ortho and para Substitution

—CF3 is a powerful EWG. It is strongly deactivating and meta directing

EWG

EWG

X

H

H

H

+

+

H

H

H

H

H

X

H

H


Many ewgs have a carbonyl group attached directly to the ring l.jpg

O

O

—CH

—CR

O

O

—COH

—COR

O

—CCl

Many EWGs Have a Carbonyl GroupAttached Directly to the Ring

All of these are meta directing and strongly deactivating

—EWG =


Other ewgs include l.jpg

—C

N

Other EWGs Include:

All of these are meta directing and strongly deactivating

—EWG =

—NO2

—SO3H


Nitration of benzaldehyde l.jpg

O2N

O

O

CH

CH

Nitration of Benzaldehyde

HNO3

H2SO4

75-84%


Problem 12 14 a page 468 l.jpg

O

O

CCl

CCl

Problem 12.14(a); page 468

Cl

Cl2

FeCl3

62%


Disulfonation of benzene l.jpg
Disulfonation of Benzene

HO3S

SO3

SO3H

H2SO4

90%


Bromination of nitrobenzene l.jpg
Bromination of Nitrobenzene

Br

Br2

NO2

NO2

Fe

60-75%


12 14 substituent effects in electrophilic aromatic substitution halogens l.jpg
12.14Substituent Effects in ElectrophilicAromatic Substitution:Halogens

F, Cl, Br, and I are ortho-para directing,but deactivating


Nitration of chlorobenzene l.jpg

Cl

Cl

Cl

Cl

NO2

NO2

NO2

Nitration of Chlorobenzene

The rate of nitration of chlorobenzene is about 30 times slower than that of benzene.

HNO3

+

+

H2SO4

30%

1%

69%


Nitration of toluene vs chlorobenzene l.jpg

CH3

42

42

2.5

2.5

58

Nitration of Toluene vs. Chlorobenzene

Cl

0.029

0.029

0.009

0.009

0.137


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