Rate and Orientation Effects in Electrophilic Aromatic Substitution - - PowerPoint PPT Presentation

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Jul 18, 2023 137 likes •318 views

Rate and Orientation Effects in Electrophilic Aromatic Substitution Reactions CH 3 CH 3 CH 3 NO 2 HNO 3 + H 2 SO 4 rate = 40 NO 2 NO 2 HNO 3 H 2 SO 4 rate = 1 CF 3 CF 3 HNO 3 H 2 SO 4 NO 2 rate = 2.5 x 10 -6 Activating Substituents Deactivating

SLIDE 1

CH3 CH3 NO2 CH3 NO2 NO2 CF3 CF3 NO2 HNO3 H2SO4 rate = 40 + HNO3 H2SO4 rate = 1 HNO3 H2SO4 rate = 2.5 x 10-6 Rate and Orientation Effects in Electrophilic Aromatic Substitution Reactions

SLIDE 2

NH2 .. X .. .. : OH .. .. S OH O O O R N H .. OH O OR O , OR .. .. O R N

O O X X X

Activating Substituents Deactivating Substituents

rtho, para

meta

rtho, para

–CN –R

SLIDE 3

Nitration of anisole The resonance donating effects of the OCH3 substituent make it an activating substituent

The aromatic ring is more nucleophilic than benzene
The resonance delocalization of the electron density of the aromatic ring is lumpy:

There is greater electron density at the o- and p- carbons

O O O O + . . .. ..

. .

.. -

SLIDE 4

Nitration of anisole:

rtho-attack of nitronium ion

O O N

+ O

O H NO2 O H NO2 O H NO2 O

H NO2 + + + +

SLIDE 5

O O N

+ O

O H NO2 O H NO2 O H NO2 O

H NO2 + + + + O O N

+ O

O H NO2 O H NO2 O H NO2 + + + +

Nitration of anisole:

rtho-attack of nitronium ion

meta-attack of nitronium ion

SLIDE 6

O O N

+ O

O H NO2 O H NO2 O H NO2 O

H NO2 + + + + O O N

+ O

O H NO2 O H NO2 O H NO2 + + + + O O N

+ O

O H NO2 O H NO2 O

H NO2 O H NO2 + + + +

Nitration of anisole:

rtho-attack of nitronium ion

meta-attack of nitronium ion para-attack of nitronium ion

SLIDE 7

O O N

+ O

O H NO2 O H NO2 O H NO2 O

H NO2 + + + + O O N

+ O

O H NO2 O H NO2 O H NO2 + + + + O O N

+ O

O H NO2 O H NO2 O

H NO2 O H NO2 + + + +

Nitration of anisole:

rtho-attack of nitronium ion

meta-attack of nitronium ion all octets filled! para-attack of nitronium ion all octets filled!

SLIDE 8

CH3O CH3O O2N CH3O NO2 CH3O NO2 + +NO2

- and p-arenium

ions + m-arenium ion

SLIDE 9

CH3O CH3O O2N CH3O NO2 CH3O NO2 + +NO2

- and p-arenium

ions + m-arenium ion

Where would the E vs reaction coordinate diagram of the nitration of benzene be placed relative to this one?

SLIDE 10

Nitration of nitrobenzene The inductive and resonance withdrawing effects of the NO2 substituent make it a deactivating substituent

The aromatic ring is less nucleophilic than benzene
The resonance delocalization of the electron density of the aromatic ring is lumpy:

There is greater electron density at the m- carbons

N O O N O O N O O N O O + + + + + + +

SLIDE 11

N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + +

Nitration of nitrobenzene:

rtho-attack of nitronium ion

SLIDE 12

N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + +

Nitration of nitrobenzene:

rtho-attack of nitronium ion

meta-attack of nitronium ion

N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + +

SLIDE 13

N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + +

Nitration of nitrobenzene:

rtho-attack of nitronium ion

meta-attack of nitronium ion para-attack of nitronium ion

N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + + N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + +

SLIDE 14

N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + + N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + + N O O O N

+ O

N O H NO2 O N O H NO2 O N O H NO2 O + + + + + + + +

Nitration of nitrobenzene:

rtho-attack of nitronium ion
meta-attack of nitronium ion

para-attack of nitronium ion

SLIDE 15

O2N O2N O2N NO2 O2N NO2 O2N + +NO2

- and p-arenium

ions + m-arenium ion

SLIDE 16

O2N O2N O2N NO2 O2N NO2 O2N + +NO2

- and p-arenium

ions + m-arenium ion

Where would the E vs reaction coordinate diagram of the nitration of benzene be placed relative to this one?

SLIDE 17

Use the same method of analysis to explain why the Cl substituent is a deactivating, o-, p-directing substituent:

Cl Cl NO2 Cl O2N 1:1 HNO3 : H2SO4 +