Consider a para-substituted benzyl cation (X), p -G-C ₆ H ₄ -CH ₂^+ , and a para-substituted benzyl anion (Y), p -G-C ₆ H ₄ -CH ₂^- . Four possible groups are available for the substituent G: -OCH ₃ , -NO ₂ , -CH ₃ , and -Cl . Which of the following pairs of substituents for G will make intermediate X the most stable, and intermediate Y the most stable, respectively?

Step-by-step solution

The stability of a carbocation (X) is increased by electron-donating groups (EDG). Among the given groups, -OCH ₃ exerts a strong +M (resonance) effect, which stabilizes the positive charge more effectively than the +H effect of -CH ₃ . Thus, X is most stable when G is -OCH ₃ . The stability of a carbanion (Y) is increased by electron-withdrawing groups (EWG). The -NO ₂ group exerts a strong -M and -I effect, which delocalizes the negative charge and provides maximum stability. Thus, Y is most stable when G is -NO