Question

Write resonance-contributing structures for the intermedicate carbocation (arenonium ion) of
(i) Phenol
(ii) Nitrobenzene with electrophile `CI^(o+)` at the
a. ortho-,
b. para-, and
c. meta-positions.

Answer 1

i.
Activing group [e.g., (-OH)` group] stabilies all `o`-positons more than `m`-postions, since the most stable `3^(@)C^(o+)` is formed when the incoming electrophile `(Cl^(o+))` enters at `o-` and `p`-positon. ltbrlt ii.
Deactivating group [eg., `(-NO_(2))` group] destlises all the positons, but does it with `o-` and `p-` positions more than `m`-position, since one resonance-contriburing structure is least stable (due to the positive charges on adjacent `C` and `N`) when incoming electrophilic `(Cl^(o+))` enters at `o-` and `p`-position. Hence electrophile attacks at `m-` positions.