JEE Main · 2024 · 04 Apr 2024 · Shift 1 · Hydrocarbons

Assign each mechanism to its electronic effect:

(A) The $-\mathrm{N}{\mathrm{H}}_2$ group releases its lone pair into the ring by resonance — a permanent electron-donating shift $\Rightarrow$ +R effect (IV).

(B) Protonation by ${\mathrm{H}}^{+}$: the reagent (an electron-deficient species) causes a temporary shift of $\pi$ electrons that occurs only in its presence $\Rightarrow$ +E effect (III).

(C) Attack by ${}^{-}\mathrm{CN}$ on the substrate, with the $\pi$ electrons shifting temporarily toward the attacking centre $\Rightarrow$ **$-$E effect (I)**.

(D) The nitro/nitroso group withdraws electrons by resonance — a permanent electron-withdrawing shift $\Rightarrow$ **$-$R effect (II)**.

Match: A-IV, B-III, C-I, D-II.