Lecture 11 - Aromatic Compounds
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General
Organic Chemistry Two credits Second Semester 2009
King Saud bin Abdulaziz University for Health Science
Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. Carey Third Edition
Instructor: Rabih O. Al-Kaysi, PhD.
Lecture 11
Chapter 6
AROMATIC COMPOUNDS
Reactions of Arenes: A Preview 1. Some reactions involve the ring. 2. In other reactions the ring is a substituent.
1. Reactions involving the ring a) Reduction Catalytic hydrogenation Birch reduction b) Electrophilic aromatic substitution c) Nucleophilic aromatic substitution 2. The ring as a substituent
Reduction Reductionof ofBenzene BenzeneRings Rings catalytic hydrogenation
H
H
H
H
H
H
H H
H H
H H
H H
H H H
Birch reduction
H
H
H
H
H
H
H H
H
The Birch Reduction
Birch BirchReduction Reductionof ofBenzene Benzene H H
H H
H
H H
H
Na, NH3
H
H
CH3OH
H
H H
H
(80%) Product is non-conjugated diene. Reaction stops here. There is no further reduction. Reaction is not hydrogenation. H2 is not involved in any way.
Oxidation of Alkylbenzenes
Site Siteof ofOxidation OxidationisisBenzylic BenzylicCarbon Carbon CH3 or CH2R or CHR2
Na2Cr2O7 H2SO4 H2O heat
O COH
Example Example O CH(CH3)2
Na2Cr2O7 H2SO4
COH
H2O heat CH3
COH O (45%)
Addition Reactions of Alkenylbenzenes •hydrogenation •halogenation •addition of hydrogen halides
Hydrogenation Hydrogenation CH3 C
CH3 CHCH3
CHCH2CH3 H2 Pt
Br
Br (92%)
Halogenation Halogenation
CH
CH2
Br2 CH
CH2
Br
Br
(82%)
Addition Addition of of Hydrogen Hydrogen Halides Halides Cl HCl
(75-84%)
Polymerization of Styrene
Polymerization Polymerization of of Styrene Styrene H2C
CH2
CH C6H5
CH2
CHC6H5
CH C6H5
polystyrene
CH2
CH C6H5
Reactions of Arenes: Electrophilic Aromatic Substitution
H δ + δ – +E Y
E +H
Y
H δ + δ – +E Y
E +H
Electrophilic Electrophilic aromatic aromatic substitutions substitutions include: include: Nitration Sulfonation Halogenation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Y
Nitration Nitrationof ofBenzene Benzene
H + HONO2
H2SO4
NO2 + H2O Nitrobenzene (95%)
Sulfonation Sulfonationof ofBenzene Benzene
H heat + HOSO2OH
SO2OH + H2O
Benzenesulfonic acid (100%)
Halogenation Halogenationof ofBenzene Benzene
H + Br2
FeBr3
Br2 + HBr Bromobenzene (65-75%)
Friedel-Crafts Friedel-CraftsAlkylation Alkylationof ofBenzene Benzene
H + (CH3)3CCl
AlCl3
C(CH3)3 + HCl
tert-Butylbenzene (60%)
Friedel-Crafts Friedel-CraftsAcylation Acylationof ofBenzene Benzene O O
AlCl3 H + CH3CH2CCl
CCH2CH3 + HCl
1-Phenyl-1-propanone (88%)
Mechanistic Principles of Electrophilic Aromatic Substitution
Step Step1: 1: attack attackof ofelectrophile electrophile on onππ -electron -electronsystem systemof ofaromatic aromaticring ring
H
H
H
E+ H
H
H
H E
H
H
+ H
highly endothermic carbocation is allylic, but not aromatic
H H
Step Step2: 2: loss lossof ofaaproton protonfrom fromthe thecarbocation carbocation intermediate intermediate
H
H
H
E H
H
H E
H
H
H+
+ H
highly exothermic this step restores aromaticity of ring
H H
Nitration of Benzene
Nitration Nitrationof ofBenzene Benzene
H + HONO2
Electrophile is nitronium ion
NO2
H2SO4
+ H2O
•• O ••
+ N
O •• ••
Step Step1: 1: attack attackof ofnitronium nitroniumcation cation on onππ -electron -electronsystem systemof ofaromatic aromaticring ring
H
H
H
NO2+ H
H
H
H NO2
H
H
+ H
H H
Step Step2: 2: loss lossof ofaaproton protonfrom fromthe thecarbocation carbocation intermediate intermediate
H
NO2
H H
H
H NO2
H
H
H+
H
+ H
H H
Halogenation of Benzene
Halogenation Halogenationof ofBenzene Benzene
H + Br2
FeBr3
Electrophile is a Lewis acid-Lewis base complex between FeBr3 and Br2.
Br2 + HBr
The 3 Complex TheBr Br2-FeBr -FeBr 2 3 Complex
••
•• Br ••
••
Br •• ••
Lewis base
+ FeBr3 Lewis acid
••
•• Br ••
+ •• Br ••
– FeBr3
Complex
The Br2-FeBr3 complex is more electrophilic than Br2 alone.
Step 3 complex Step1: 1: attack attackof ofBr Br2-FeBr -FeBr 2 3 complex on onππ -electron -electronsystem systemof ofaromatic aromaticring ring
H
H
H
Br H
H
H
+ Br
– FeBr3
H Br
H
H
+ H
H H
+ FeBr4–
Step Step2: 2: loss lossof ofaaproton protonfrom fromthe thecarbocation carbocation intermediate intermediate
H
H
Br H
H
H Br
H
H
H+
H
+ H
H H
Rate and Regioselectivity in Electrophilic Aromatic Substitution
A substituent already present on the ring can affect both the rate and regioselectivity of electrophilic aromatic substitution.
Effect Effecton onRate Rate Activating substituents increase the rate of EAS compared to that of benzene. Deactivating substituents decrease the rate of EAS compared to benzene.
Methyl MethylGroup Group
CH3
Toluene undergoes nitration 20-25 times faster than benzene. A methyl group is an activating substituent.
Trifluoromethyl TrifluoromethylGroup Group
CF3
(Trifluoromethyl)benzene undergoes nitration 40,000 times more slowly than benzene . A trifluoromethyl group is a deactivating substituent.
Effect Effecton onRegioselectivity Regioselectivity Ortho-para directors direct an incoming electrophile to positions ortho and/or para to themselves. Meta directors direct an incoming electrophile to positions meta to themselves.
Nitration Nitrationof ofToluene Toluene CH3
CH3
CH3
CH3
NO2
HNO3
+
acetic anhydride
+ NO2 NO2
63%
3%
34%
o- and p-nitrotoluene together comprise 97% of the product a methyl group is an ortho-para director
Nitration Nitrationof of(Trifluoromethyl)benzene (Trifluoromethyl)benzene CF3
CF3
CF3
CF3
NO2
HNO3
+
H2SO4
+ NO2 NO2
6%
91%
m-nitro(trifluoromethyl)benzene comprises 91% of the product a trifluoromethyl group is a meta director
3%
Rate and Regioselectivity in the Nitration of Toluene
Carbocation CarbocationStability StabilityControls ControlsRegioselectivity Regioselectivity
CH3 H
NO2
+
H H
gives ortho
H H
CH3 H H
+ H
NO2
gives para
CH3 H
H
H
H
+
H
H H NO2
gives meta
Carbocation CarbocationStability StabilityControls ControlsRegioselectivity Regioselectivity
CH3 H
NO2 H
+
H
H
CH3 H +
H
H
H gives ortho
NO2
gives para
more stable
CH3 H
H
H
H
+
H
H H NO2
gives meta less stable
ortho orthoNitration Nitrationof ofToluene Toluene CH3 H +
H H
NO2 H H
ortho orthoNitration Nitrationof ofToluene Toluene CH3 H +
H H
NO2 H H
CH3 H H
NO2 H
+
H H
ortho orthoNitration Nitrationof ofToluene Toluene CH3 H +
H H
NO2 H H
CH3 H H
NO2 H
+
H H
CH3 H H
+
NO2 H H
H this resonance form is a tertiary carbocation
ortho orthoNitration Nitrationof ofToluene Toluene CH3 H +
H H
NO2 H H
CH3 H H
NO2 H
+
H H
CH3 H
NO2
+
H
H H
H
the rate-determining intermediate in the ortho nitration of toluene has tertiary carbocation character
para paraNitration Nitrationof ofToluene Toluene CH3 H H
H + H
H NO2
para paraNitration Nitrationof ofToluene Toluene CH3 H H
+ H
NO2
CH3 H
H
H
H
H
+
H H
NO2
this resonance form is a tertiary carbocation
para paraNitration Nitrationof ofToluene Toluene CH3 H H
CH3 H
+ H
H NO2
H
CH3 H H
+
H
H +
H H H
NO2
this resonance form is a tertiary carbocation
H
NO2
H
para paraNitration Nitrationof ofToluene Toluene CH3 H H
CH3 H
+ H
H NO2
H
CH3 H H
+
H
H +
H H H
NO2
H
NO2
the rate-determining intermediate in the para nitration of toluene has tertiary carbocation character
H
meta metaNitration Nitrationof ofToluene Toluene CH3 H
+
H H
H H NO2
meta metaNitration Nitrationof ofToluene Toluene CH3 H
+
H H
CH3 H
H
H NO2
H
H
+
H
H NO2
meta metaNitration Nitrationof ofToluene Toluene CH3 H H
+
CH3 H
H
H NO2
H
+
CH3 H
H
H NO2
H
H +
H H H all the resonance forms of the ratedetermining intermediate in the meta nitration of toluene have their positive charge on a secondary carbon
H NO2
Nitration Nitrationof ofToluene: Toluene: Interpretation Interpretation • The rate-determining intermediates for ortho and para nitration each have a resonance form that is a tertiary carbocation. All of the resonance forms for the rate-determining intermediate in meta nitration are secondary carbocations. • Tertiary carbocations, being more stable, are formed faster than secondary ones. Therefore, the intermediates for attack at the ortho and para positions are formed faster than the intermediate for attack at the meta position. This explains why the major products are o- and p-nitrotoluene.
Nitration Nitrationof ofToluene: Toluene: Partial PartialRate RateFactors Factors • The experimentally determined reaction rate can be combined with the ortho/meta/para distribution to give partial rate factors for substitution at the various ring positions. • Expressed as a numerical value, a partial rate factor tells you by how much the rate of substitution at a particular position is faster (or slower) than at a single position of benzene.
Rate and Regioselectivity in the Nitration of (Trifluoromethyl)benzene
AAKey KeyPoint Point
H3C
C+
F3C
C+
A methyl group is electron-donating and stabilizes a carbocation. Because F is so electronegative, a CF3 group destabilizes a carbocation.
Carbocation CarbocationStability StabilityControls ControlsRegioselectivity Regioselectivity
CF3 H
NO2
+
H H
gives ortho
H H
CF3 H H
+ H
NO2
gives para
CF3 H
H
H
H
+
H
H H NO2
gives meta
Carbocation CarbocationStability StabilityControls ControlsRegioselectivity Regioselectivity
CF3 H
NO2 H
+
H
H
CF3 H H
+ H
H gives ortho less stable
NO2
gives para
CF3 H
H
H
H
+
H
H H NO2
gives meta more stable
Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents
Table Table12.2 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 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 Electron-ReleasingGroups Groups(ERGs) (ERGs) are ortho-para directing and activating ERG
ERGs include —R, —Ar, and —C=C
Electron-Releasing Electron-ReleasingGroups Groups(ERGs) (ERGs) are ortho-para directing and strongly activating ERG
ERGs such as —OH, and —OR are strongly activating
Nitration Nitrationof ofPhenol Phenol occurs about 1000 times faster than nitration of benzene OH
OH
OH NO2
HNO3
+ NO2 44%
56%
Bromination Brominationof ofAnisole Anisole FeBr3 catalyst not necessary OCH3
OCH3 Br2 acetic acid
Br 90%
Electron-Releasing Electron-ReleasingGroups Groups(ERGs) (ERGs) •• ERG
ERGs with a lone pair on the atom directly attached to the ring are ortho-para directing and strongly activating
Examples Examples O •• ERG =
•• •• OH
••
•• OR
••
•• OCR
O •• NH2
•• NHR
•• NR2
•• NHCR
All of these are ortho-para directing and strongly to very strongly activating
Organic Chemistry Two credits Second Semester 2009
King Saud bin Abdulaziz University for Health Science
Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. Carey Third Edition
Instructor: Rabih O. Al-Kaysi, PhD.
Lecture 11
Chapter 6
AROMATIC COMPOUNDS
Reactions of Arenes: A Preview 1. Some reactions involve the ring. 2. In other reactions the ring is a substituent.
1. Reactions involving the ring a) Reduction Catalytic hydrogenation Birch reduction b) Electrophilic aromatic substitution c) Nucleophilic aromatic substitution 2. The ring as a substituent
Reduction Reductionof ofBenzene BenzeneRings Rings catalytic hydrogenation
H
H
H
H
H
H
H H
H H
H H
H H
H H H
Birch reduction
H
H
H
H
H
H
H H
H
The Birch Reduction
Birch BirchReduction Reductionof ofBenzene Benzene H H
H H
H
H H
H
Na, NH3
H
H
CH3OH
H
H H
H
(80%) Product is non-conjugated diene. Reaction stops here. There is no further reduction. Reaction is not hydrogenation. H2 is not involved in any way.
Oxidation of Alkylbenzenes
Site Siteof ofOxidation OxidationisisBenzylic BenzylicCarbon Carbon CH3 or CH2R or CHR2
Na2Cr2O7 H2SO4 H2O heat
O COH
Example Example O CH(CH3)2
Na2Cr2O7 H2SO4
COH
H2O heat CH3
COH O (45%)
Addition Reactions of Alkenylbenzenes •hydrogenation •halogenation •addition of hydrogen halides
Hydrogenation Hydrogenation CH3 C
CH3 CHCH3
CHCH2CH3 H2 Pt
Br
Br (92%)
Halogenation Halogenation
CH
CH2
Br2 CH
CH2
Br
Br
(82%)
Addition Addition of of Hydrogen Hydrogen Halides Halides Cl HCl
(75-84%)
Polymerization of Styrene
Polymerization Polymerization of of Styrene Styrene H2C
CH2
CH C6H5
CH2
CHC6H5
CH C6H5
polystyrene
CH2
CH C6H5
Reactions of Arenes: Electrophilic Aromatic Substitution
H δ + δ – +E Y
E +H
Y
H δ + δ – +E Y
E +H
Electrophilic Electrophilic aromatic aromatic substitutions substitutions include: include: Nitration Sulfonation Halogenation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Y
Nitration Nitrationof ofBenzene Benzene
H + HONO2
H2SO4
NO2 + H2O Nitrobenzene (95%)
Sulfonation Sulfonationof ofBenzene Benzene
H heat + HOSO2OH
SO2OH + H2O
Benzenesulfonic acid (100%)
Halogenation Halogenationof ofBenzene Benzene
H + Br2
FeBr3
Br2 + HBr Bromobenzene (65-75%)
Friedel-Crafts Friedel-CraftsAlkylation Alkylationof ofBenzene Benzene
H + (CH3)3CCl
AlCl3
C(CH3)3 + HCl
tert-Butylbenzene (60%)
Friedel-Crafts Friedel-CraftsAcylation Acylationof ofBenzene Benzene O O
AlCl3 H + CH3CH2CCl
CCH2CH3 + HCl
1-Phenyl-1-propanone (88%)
Mechanistic Principles of Electrophilic Aromatic Substitution
Step Step1: 1: attack attackof ofelectrophile electrophile on onππ -electron -electronsystem systemof ofaromatic aromaticring ring
H
H
H
E+ H
H
H
H E
H
H
+ H
highly endothermic carbocation is allylic, but not aromatic
H H
Step Step2: 2: loss lossof ofaaproton protonfrom fromthe thecarbocation carbocation intermediate intermediate
H
H
H
E H
H
H E
H
H
H+
+ H
highly exothermic this step restores aromaticity of ring
H H
Nitration of Benzene
Nitration Nitrationof ofBenzene Benzene
H + HONO2
Electrophile is nitronium ion
NO2
H2SO4
+ H2O
•• O ••
+ N
O •• ••
Step Step1: 1: attack attackof ofnitronium nitroniumcation cation on onππ -electron -electronsystem systemof ofaromatic aromaticring ring
H
H
H
NO2+ H
H
H
H NO2
H
H
+ H
H H
Step Step2: 2: loss lossof ofaaproton protonfrom fromthe thecarbocation carbocation intermediate intermediate
H
NO2
H H
H
H NO2
H
H
H+
H
+ H
H H
Halogenation of Benzene
Halogenation Halogenationof ofBenzene Benzene
H + Br2
FeBr3
Electrophile is a Lewis acid-Lewis base complex between FeBr3 and Br2.
Br2 + HBr
The 3 Complex TheBr Br2-FeBr -FeBr 2 3 Complex
••
•• Br ••
••
Br •• ••
Lewis base
+ FeBr3 Lewis acid
••
•• Br ••
+ •• Br ••
– FeBr3
Complex
The Br2-FeBr3 complex is more electrophilic than Br2 alone.
Step 3 complex Step1: 1: attack attackof ofBr Br2-FeBr -FeBr 2 3 complex on onππ -electron -electronsystem systemof ofaromatic aromaticring ring
H
H
H
Br H
H
H
+ Br
– FeBr3
H Br
H
H
+ H
H H
+ FeBr4–
Step Step2: 2: loss lossof ofaaproton protonfrom fromthe thecarbocation carbocation intermediate intermediate
H
H
Br H
H
H Br
H
H
H+
H
+ H
H H
Rate and Regioselectivity in Electrophilic Aromatic Substitution
A substituent already present on the ring can affect both the rate and regioselectivity of electrophilic aromatic substitution.
Effect Effecton onRate Rate Activating substituents increase the rate of EAS compared to that of benzene. Deactivating substituents decrease the rate of EAS compared to benzene.
Methyl MethylGroup Group
CH3
Toluene undergoes nitration 20-25 times faster than benzene. A methyl group is an activating substituent.
Trifluoromethyl TrifluoromethylGroup Group
CF3
(Trifluoromethyl)benzene undergoes nitration 40,000 times more slowly than benzene . A trifluoromethyl group is a deactivating substituent.
Effect Effecton onRegioselectivity Regioselectivity Ortho-para directors direct an incoming electrophile to positions ortho and/or para to themselves. Meta directors direct an incoming electrophile to positions meta to themselves.
Nitration Nitrationof ofToluene Toluene CH3
CH3
CH3
CH3
NO2
HNO3
+
acetic anhydride
+ NO2 NO2
63%
3%
34%
o- and p-nitrotoluene together comprise 97% of the product a methyl group is an ortho-para director
Nitration Nitrationof of(Trifluoromethyl)benzene (Trifluoromethyl)benzene CF3
CF3
CF3
CF3
NO2
HNO3
+
H2SO4
+ NO2 NO2
6%
91%
m-nitro(trifluoromethyl)benzene comprises 91% of the product a trifluoromethyl group is a meta director
3%
Rate and Regioselectivity in the Nitration of Toluene
Carbocation CarbocationStability StabilityControls ControlsRegioselectivity Regioselectivity
CH3 H
NO2
+
H H
gives ortho
H H
CH3 H H
+ H
NO2
gives para
CH3 H
H
H
H
+
H
H H NO2
gives meta
Carbocation CarbocationStability StabilityControls ControlsRegioselectivity Regioselectivity
CH3 H
NO2 H
+
H
H
CH3 H +
H
H
H gives ortho
NO2
gives para
more stable
CH3 H
H
H
H
+
H
H H NO2
gives meta less stable
ortho orthoNitration Nitrationof ofToluene Toluene CH3 H +
H H
NO2 H H
ortho orthoNitration Nitrationof ofToluene Toluene CH3 H +
H H
NO2 H H
CH3 H H
NO2 H
+
H H
ortho orthoNitration Nitrationof ofToluene Toluene CH3 H +
H H
NO2 H H
CH3 H H
NO2 H
+
H H
CH3 H H
+
NO2 H H
H this resonance form is a tertiary carbocation
ortho orthoNitration Nitrationof ofToluene Toluene CH3 H +
H H
NO2 H H
CH3 H H
NO2 H
+
H H
CH3 H
NO2
+
H
H H
H
the rate-determining intermediate in the ortho nitration of toluene has tertiary carbocation character
para paraNitration Nitrationof ofToluene Toluene CH3 H H
H + H
H NO2
para paraNitration Nitrationof ofToluene Toluene CH3 H H
+ H
NO2
CH3 H
H
H
H
H
+
H H
NO2
this resonance form is a tertiary carbocation
para paraNitration Nitrationof ofToluene Toluene CH3 H H
CH3 H
+ H
H NO2
H
CH3 H H
+
H
H +
H H H
NO2
this resonance form is a tertiary carbocation
H
NO2
H
para paraNitration Nitrationof ofToluene Toluene CH3 H H
CH3 H
+ H
H NO2
H
CH3 H H
+
H
H +
H H H
NO2
H
NO2
the rate-determining intermediate in the para nitration of toluene has tertiary carbocation character
H
meta metaNitration Nitrationof ofToluene Toluene CH3 H
+
H H
H H NO2
meta metaNitration Nitrationof ofToluene Toluene CH3 H
+
H H
CH3 H
H
H NO2
H
H
+
H
H NO2
meta metaNitration Nitrationof ofToluene Toluene CH3 H H
+
CH3 H
H
H NO2
H
+
CH3 H
H
H NO2
H
H +
H H H all the resonance forms of the ratedetermining intermediate in the meta nitration of toluene have their positive charge on a secondary carbon
H NO2
Nitration Nitrationof ofToluene: Toluene: Interpretation Interpretation • The rate-determining intermediates for ortho and para nitration each have a resonance form that is a tertiary carbocation. All of the resonance forms for the rate-determining intermediate in meta nitration are secondary carbocations. • Tertiary carbocations, being more stable, are formed faster than secondary ones. Therefore, the intermediates for attack at the ortho and para positions are formed faster than the intermediate for attack at the meta position. This explains why the major products are o- and p-nitrotoluene.
Nitration Nitrationof ofToluene: Toluene: Partial PartialRate RateFactors Factors • The experimentally determined reaction rate can be combined with the ortho/meta/para distribution to give partial rate factors for substitution at the various ring positions. • Expressed as a numerical value, a partial rate factor tells you by how much the rate of substitution at a particular position is faster (or slower) than at a single position of benzene.
Rate and Regioselectivity in the Nitration of (Trifluoromethyl)benzene
AAKey KeyPoint Point
H3C
C+
F3C
C+
A methyl group is electron-donating and stabilizes a carbocation. Because F is so electronegative, a CF3 group destabilizes a carbocation.
Carbocation CarbocationStability StabilityControls ControlsRegioselectivity Regioselectivity
CF3 H
NO2
+
H H
gives ortho
H H
CF3 H H
+ H
NO2
gives para
CF3 H
H
H
H
+
H
H H NO2
gives meta
Carbocation CarbocationStability StabilityControls ControlsRegioselectivity Regioselectivity
CF3 H
NO2 H
+
H
H
CF3 H H
+ H
H gives ortho less stable
NO2
gives para
CF3 H
H
H
H
+
H
H H NO2
gives meta more stable
Substituent Effects in Electrophilic Aromatic Substitution: Activating Substituents
Table Table12.2 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 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 Electron-ReleasingGroups Groups(ERGs) (ERGs) are ortho-para directing and activating ERG
ERGs include —R, —Ar, and —C=C
Electron-Releasing Electron-ReleasingGroups Groups(ERGs) (ERGs) are ortho-para directing and strongly activating ERG
ERGs such as —OH, and —OR are strongly activating
Nitration Nitrationof ofPhenol Phenol occurs about 1000 times faster than nitration of benzene OH
OH
OH NO2
HNO3
+ NO2 44%
56%
Bromination Brominationof ofAnisole Anisole FeBr3 catalyst not necessary OCH3
OCH3 Br2 acetic acid
Br 90%
Electron-Releasing Electron-ReleasingGroups Groups(ERGs) (ERGs) •• ERG
ERGs with a lone pair on the atom directly attached to the ring are ortho-para directing and strongly activating
Examples Examples O •• ERG =
•• •• OH
••
•• OR
••
•• OCR
O •• NH2
•• NHR
•• NR2
•• NHCR
All of these are ortho-para directing and strongly to very strongly activating
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