Substituent Effects sections 12'912'16

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Substituent Effects(sections 12.9-12.16)
What is the reactivity and orientation for
alkylation of a monosubstituted benzene like
nitrobenzene?
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Substituent Effects

• 1. Some groups make the ring more reactive
• 2. Some groups make the ring less reactive
• 3. Some groups direct to the o p position
• 4. Some groups direct to the m position

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Rules for Substituent Effects

• 1. All activators will be o, p-directors
• 2. All deactivators will be m- directors
• except for the halogens

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Maps Showing Substituent Effects
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Nitration of Toluene
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Nitration of Toluene


34
3
63
9
Nitration of (Trifluoromethyl)benzene
10
Nitration of (Trifluoromethyl)benzene


3
91
6
11
Carbocation Stability Controls Regioselectivity
gives ortho
gives para
gives meta
12
ortho Nitration of Toluene
CH3
NO2
H
H
H
H
H

• this resonance form is a tertiary carbocation

13
ortho Nitration of Toluene
CH3
CH3
CH3
NO2
NO2
NO2
H
H
H

H
H
H

H
H
H
H
H
H
H
H
H
14
ortho Nitration of (Trifluoromethyl)benzene

• this resonance form is destabilized

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para Nitration of Toluene

• this resonance form is a tertiary carbocation

16
para Nitration of Toluene

• the rate-determining intermediate in the
  paranitration of toluene has tertiary
  carbocation character

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meta Nitration of Toluene

• all the resonance forms of the rate-determining
  intermediate in the meta nitration of toluene
  have their positive charge on a secondary carbon