Question

Which of the following is the correct order of electron density on the benzene ring in the following compounds?

• A. $II>III>I$
• B. $I>III>II$
• C. $I>II>III$
• D. $III>II>I$

Answer 1

The correct option is C $I>II>III$

In case of Halogens, I effect dominates over M effect. Hence they are electron-withdrawing in nature. The overall withdrawing power of Cl is more than F when attached to conjugated system even though F is more electronegative.

$-Cl$ shows $+Mand-I$ effects. In case of $-Cl,+M$ weakens up due to $2p-3p$ overlapping. But it is not so in case of $-F$ which involves $2p-2p$ overlap which is more effective. So, $+M$ effect of $-F$ is more than $-Cl$.

Therefore, the correct order of electron density is:
$I>II>III$