16. Chemistry of Benzene: Electrophilic Aromatic Substitution Part 2

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16. Chemistry of Benzene Electrophilic Aromatic
Substitution Part 2

• Based on
• McMurrys Organic Chemistry, 6th edition, Chapter
  16

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Reaction of Disubstituted Benzenes
When you have two or more substituents, where on
the benzene ring will the substitution reaction
occur?
The orientation will depend on - directing
power of each substituent - steric effects
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Disubstituted Benzenes Directing Power

• Case AIf the directing effects of the two groups
  are the same, the result is additive.

-Me is an o/p director
-NO2 is a meta director
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Disubstituted Benzenes Directing Power
Case BIf directing effects of the groups oppose
each other, then the more powerful activating
group decides the outcome. (Mixtures of products
may occationally result.)
-OH ismorepowerful
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Directing Power Which groups control?
The strongest activators are also the strongest
directors.
Strongest directing groups
Weakest directing groups
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Directing Power Which groups control?
We will classify substituents into three groups,
according to their ability to direct the site of
reaction.
Class I -OH, -OR, and -NR2 groups Class
II alkyl and halogen Class III all meta
directors
STRONGEST
WEAKEST
Example
The amino substituent is in Class I, so it
controls the orientation.(The methyl group is in
Class II.)
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Reaction of Disubstituted Benzenes
When you have two or more substituents, where on
the benzene ring will the substitution reaction
occur?
The orientation will depend on - directing
power of each substituent - steric effects