23
12.12 12.12 Substituent Effects in Substituent Effects in Electrophilic Electrophilic Aromatic Substitution: Aromatic Substitution: Activating Substituents Activating Substituents

12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

Embed Size (px)

Citation preview

Page 1: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

12.1212.12Substituent Effects in ElectrophilicSubstituent Effects in Electrophilic

Aromatic Substitution:Aromatic Substitution:Activating SubstituentsActivating Substituents

Page 2: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

Table 12.2Table 12.2

Very strongly activatingVery strongly activating

Strongly activatingStrongly activating

ActivatingActivating

Standard of comparison is HStandard of comparison is H

DeactivatingDeactivating

Strongly deactivatingStrongly deactivating

Very strongly deactivatingVery strongly deactivating

Classification of Substituents in Electrophilic Classification of Substituents in Electrophilic

Aromatic Substitution ReactionsAromatic Substitution Reactions

Page 3: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

1. All activating substituents are 1. All activating substituents are ortho-para directors.ortho-para directors.

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

3. Strongly deactivating substituents are 3. Strongly deactivating substituents are meta directors.meta directors.

GeneralizationsGeneralizations

Page 4: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

are ortho-para directing and activatingare ortho-para directing and activating

ERGERG

ERGs include —R, —Ar, and —C=CERGs include —R, —Ar, and —C=C

Electron-Releasing Groups (ERGs)Electron-Releasing Groups (ERGs)

Page 5: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

are ortho-para directing and strongly activatingare ortho-para directing and strongly activating

ERGERG

ERGs such as —OH, and —OR areERGs such as —OH, and —OR arestrongly activatingstrongly activating

Electron-Releasing Groups (ERGs)Electron-Releasing Groups (ERGs)

Page 6: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

occurs about 1000 times faster than nitration occurs about 1000 times faster than nitration of benzeneof benzene

OHOH

HNOHNO33

OHOH

NONO22

OHOH

NONO22

++

44%44% 56%56%

Nitration of PhenolNitration of Phenol

Page 7: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

FeBrFeBr33 catalyst not necessary catalyst not necessary

OCHOCH33

BrBr22

OCHOCH33

BrBr

90%90%

aceticaceticacidacid

Bromination of AnisoleBromination of Anisole

Page 8: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

++

HH

HH

HH

HH

HH

BrBr

OCHOCH33••••••••

HH

HH

HH

HH

HH

BrBr

++

OCHOCH33••••••••

HH

HH

HH

HH

HH

BrBr

++ OCHOCH33••••

Oxygen Lone Pair Stabilizes IntermediateOxygen Lone Pair Stabilizes Intermediate

all atomsall atomshave octetshave octets

Page 9: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

ERGs with a lone pair on the atom directlyERGs with a lone pair on the atom directlyattached to the ring are ortho-para directingattached to the ring are ortho-para directing

and strongly activatingand strongly activating

ERGERG

Electron-Releasing Groups (ERGs)Electron-Releasing Groups (ERGs)

••••

Page 10: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

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

ExamplesExamples

ERG = ERG = •••• ••••OH OH ••••

OR OR ••••••••

OCR OCR ••••••••

OO

•••• NHNH22 NHCR NHCR ••••

OO

••••NHR NHR •••• NRNR22

Page 11: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

Lone Pair Stabilizes Intermediates forLone Pair Stabilizes Intermediates forortho and para Substitutionortho and para Substitution

comparable stabilization not possible for comparable stabilization not possible for intermediate leading to meta substitutionintermediate leading to meta substitution

HH

HH

HH

HH

HH

XX

++ ERGERG

HH

HH

HH

HH

HH

XX

++ ERGERG

Page 12: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

12.1312.13Substituent Effects in ElectrophilicSubstituent Effects in Electrophilic

Aromatic Substitution:Aromatic Substitution:Strongly Deactivating SubstituentsStrongly Deactivating Substituents

Page 13: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

ERGs Stabilize Intermediates forERGs Stabilize Intermediates forortho and para Substitutionortho and para Substitution

HH

HH

HH

HH

HH

XX

++

ERGERG••••

HH

HH

HH

HH

HH

XX

++

ERGERG••••

Page 14: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

Electron-withdrawing Groups (EWGs) DestabilizeElectron-withdrawing Groups (EWGs) DestabilizeIntermediates for ortho and para SubstitutionIntermediates for ortho and para Substitution

HH

HH

HH

HH

HH

XX

++

EWGEWG

HH

HH

HH

HH

HH

XX

++

EWGEWG

——CFCF33 is a powerful EWG. It is strongly is a powerful EWG. It is strongly

deactivating and meta directingdeactivating and meta directing

Page 15: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

All of these are meta directing and strongly deactivatingAll of these are meta directing and strongly deactivating

Many EWGs Have a Carbonyl GroupMany EWGs Have a Carbonyl GroupAttached Directly to the RingAttached Directly to the Ring

——EWG = EWG =

OO

——CHCH

OO

——CRCR

OO

——COHCOH

OO

——CORCOR

OO

——CClCCl

Page 16: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

All of these are meta directing and strongly deactivatingAll of these are meta directing and strongly deactivating

Other EWGs Include:Other EWGs Include:

——EWG = EWG = ——NONO22

——SOSO33HH

——CC NN

Page 17: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

HNOHNO33

75-84%75-84%

Nitration of BenzaldehydeNitration of Benzaldehyde

CHCH

OO

HH22SOSO44

CHCH

OOOO22NN

Page 18: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

ClCl22

62%62%

Problem 12.14(a); page 468Problem 12.14(a); page 468

CClCCl

OO

FeClFeCl33

CClCCl

OOClCl

Page 19: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

SOSO33

90%90%

Disulfonation of BenzeneDisulfonation of Benzene

HH22SOSO44

SOSO33HH

HOHO33SS

Page 20: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

BrBr22

60-75%60-75%

Bromination of NitrobenzeneBromination of Nitrobenzene

FeFe

BrBr

NONO22 NONO22

Page 21: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

12.1412.14Substituent Effects in ElectrophilicSubstituent Effects in Electrophilic

Aromatic Substitution:Aromatic Substitution:HalogensHalogens

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

Page 22: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

Nitration of ChlorobenzeneNitration of Chlorobenzene

ClCl

HNOHNO33

ClCl

NONO22

ClCl

NONO22

ClCl

NONO22

++ ++

69%69%1%1%30%30%

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

HH22SOSO44

Page 23: 12.12 Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents

Nitration of Toluene vs. ChlorobenzeneNitration of Toluene vs. Chlorobenzene

CHCH33

4242

2.52.5

5858

4242

2.52.5

0.1370.137

0.0090.009

0.0290.029

ClCl

0.0290.029

0.0090.009