Question

The only $o,$ $p-$directing group which is deactivating in nature is:

• A. $-N{H}_2$
• B. $-OH$
• C. $-X$ (halogens)
• D. $-R$ (alkyl groups)

Answer 1

Answer: (C)

$-X$ (halogens)

Halides are ortho-para- directing groups but unlike most ortho-para- directors halides tend to deactivate benzene. This unusual behaviour can be explained by two properties:

1. Since the halogens are very electronegative they cause inductive withdrawal (withdrawal of electrons from the carbon atom of benzene).

2. Since the halogens have non-bonding electrons they can donate electron density through pi bonding (resonance donation).

Option C is correct.