JEE Main · 2023 · 30 Jan 2023 · Shift 2 · General Organic Chemistry

A positive charge created on a carbon of the aniline ring can be quenched only if the lone pair on nitrogen is able to reach that carbon through the ring $\pi$ system. Such donation is geometrically possible when the electron-deficient carbon lies ortho or para to the amino-bearing carbon; the lone pair then flows in and the cation is rewritten as a closed-shell iminium, $>\mathrm{C}=\stackrel{\oplus }{\mathrm{N}}{\mathrm{H}}_2$, in which nitrogen carries the charge and every atom holds a complete octet. When the charge sits meta to the amino group no such resonance path exists and the ion is left a bare, poorly stabilised carbocation. Maximum stabilisation therefore accompanies the ion whose empty centre lies next to the amino-substituted carbon, where the nitrogen lone pair closes directly onto it to form the stable iminium ion.