Organic Chemistry

Section 16.16 Electrophilic Substitution Reactions of Naphthalene and Substituted Naphthalenes 659

irreversible (mild reaction conditions). The 2-substituted product is the thermodynamic
product because it is more stable. It is the predominant product when the reaction is
carried out under conditions that cause it to be reversible (higher temperatures).
The 1-substituted product is easier to form because the carbocation leading to its
formation is more stable. The 2-substituted product is more stable because there is
more room for the bulky sulfonic acid group at the 2-position. In the 1-substituted
product, the sulfonic acid group is too close to the hydrogen at the 8-position.

In the case of substituted naphthalenes, the nature of the substituent determines
which ring will undergo electrophilic substitution. If the substituent is deactivating,
the electrophile will attack the 1-position of the ring that lacks the deactivating sub-
stituent, because that ring is more reactive than the ring that contains the deactivating
substituent.

If the substituent is activating, the electrophile will attack the ring that contains the sub-
stituent. The incoming electrophile will be directed to a 1-position that is ortho or para to
the substituent, because all activating substituents are ortho–para directors (Section 16.4).

PROBLEM 35

Give the products that would be obtained from the reaction of the following compounds

with

a. c.

b. d.

NO 2

Br

CH 3

OCH 3

Cl 2 :

CH 3 CH 3

++CH 3 CCl HCl

1. AlCl 3

OCH 3 OCH 3

CH 3 C O

++Br 2 HBr

Br

O

2. H 2 O

+ HNO 3

H 2 SO 4

NO 2 NO 2

NO 2

H SO 3 H H

SO 3 H

H

an unfavorable

steric interaction

1-Substituted naphthalenes are easier to

form; 2-substituted naphthalenes are

more stable.

Tutorial:

Terms for the reactions of

substituted benzenes