Organic Chemistry

Monosubstituted Benzenes

Group Strength Directing

-NH 2 , -NHR, -NRR very strong ortho/para

-OH, -O- very strong ortho/para

-NHCOCH 3 , -NHCOR strong ortho/para

-OCH 3 , -OR strong ortho/para

-CH 3 , -C 2 H 5 , -R weak ortho/para

-C 6 H 5 very weak ortho/para

72.3 Deactivating Substituents

A deactivating group is a functional group attached to a benzene molecule that removes
electron density from the benzene ring, making electrophilic aromatic substitution reac-
tions slower and more difficult than they would be on benzene alone. As discussed above
for activating groups, deactivating groups may also determine the positions (relative to
themselves) on the benzene ring where substitutions take place, so each deactivating group
is listed below along with its directing characteristic.

Group Strength Directing

-NR 3 + very strong meta

-NO 2 very strong meta

-CF 3 , CCl 3 very strong meta

-CN strong meta

-SO 3 H strong meta

-CO 2 H, -CO 2 R strong meta

-COH, -COR strong meta

-F weak ortho/para

-Cl weak ortho/para

-Br weak ortho/para

72.4 Activation vs. Deactivation and ortho/para vs. meta directing

So why are some substituents activating or deactivating? Why are some meta directing
and others ortho/para directing? From the above tables, it seems pretty clear there’s a
relationship.

There are primarily two effects that substituents impart on the ring that affect these fea-
tures:

1. Resonance effects


2. Inductive effects