Question

Which one of the following groups can exert both $+M$ and $-I$ effect?

• A. $-CHO$
• B. $-N{O}_2$
• C. $-Cl$
• D. $-C{H}_3$

Answer 1

Answer: (C)

$-Cl$

Inductive effect is an electronic effect due to the polarisation of $\sigma$ bonds within a molecule or ion. It is mainly due to the electronegativity difference between the atoms on either side of the bond. $Cl$ atom exerts $-I$ effect as it is highly electronegative in nature and therefore, withdraws electron density. However, due to the presence of lone pair of electrons on it, it can also donate electron density leading to various resonating structures in aromatic compounds. This effect is known as $+M$ effect.

Hence, $-Cl$ group can exert both $-I$ and $+M$ effect.