JEE Main · 2017 · 02 Apr 2017 · Offline · Hydrocarbons

In the strongly acidic nitrating mixture of concentrated $HN{O}_3$ and $H_{2}S{O}_4$, aniline is largely protonated to the anilinium ion, $-N{H}_3^{+}$. This positively charged group is strongly deactivating and meta-directing, so nitration of the anilinium ion delivers a significant proportion of the meta-nitro product (about $47\%$). The other three compounds keep ortho/para-directing groups under these conditions — phenol ($-OH$), phenyl acetate ($-OCOC{H}_3$) and acetanilide ($-NHCOC{H}_3$) each direct the incoming nitro group mainly to the ortho and para positions — so only aniline gives an appreciable amount of the meta product.