Question

The structure of intemediate obtained after the attack of $B{r}^{+}$ on anilinium ion is:

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

Attack of an electrophile results in the formation of arenium ion which is also known as Wheland's intermediate. This is also called sigma complex and this intermediate will have $s{p}^3$ carbon in the benzene ring and stops the cyclic resonance. This intermediate is non-aromatic due to presence of $s{p}^3$ carbon.
The $N{H}_3^{+}$ group in anilinium ion is a meta directing group because of its electron withdrawing nature (-I effect). Thus bromination of anilinium ion, will result in the attack of $B{r}^{+}$ at the meta position to form wheland intermediate.

Only in option (b) and (d), bromination is occurs at meta position.

Electrophile attacked carbon will be a $s{p}^3$ carbon, thus delocalisation of electrons does not occurs at the meta position carbon.
Therefore, intermediate in option (d) is wrong.
Thus, option (b) represent the correct wheland intermediate structure for nitration of anilinium ion.