Chemistry - GOC Question with Solution | TestHub

(A) 1-Methylcyclopentene has hyperconjugation ($\mathrm{C}{\mathrm{H}}_3$ and ring $\mathrm{C}-\mathrm{H}$ next to $\mathrm{C}=\mathrm{C}$) and the inductive effect, but only one $\mathrm{C}=\mathrm{C}$ with no conjugation: no resonance.

(B) $-\mathrm{CN}$ is on an $\mathrm{s}{\mathrm{p}}^3$ carbon, so it is not conjugated with the two isolated $\mathrm{C}=\mathrm{C}$ bonds: no resonance. There is also no $\mathrm{C}{\mathrm{H}}_3$.

(C) The $-\mathrm{OH}$ and $-\mathrm{C}{\mathrm{H}}_3$ are on an $\mathrm{s}{\mathrm{p}}^3$ carbon and the two $\mathrm{C}=\mathrm{C}$ are isolated: no resonance.

(D) 4-Methylbenzaldehyde has the inductive effect ($\mathrm{C}=\mathrm{O}$, ring), hyperconjugation ($\mathrm{C}{\mathrm{H}}_3$ on the ring) and resonance (ring conjugated with $\mathrm{CHO}$).

Answer: (D).