See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: The effect of solvent polarity on reaction rate depends on the charge development or charge dispersal in the transition state relative to the reactants. Reaction A: Nu + R-L --> Nu(+)-R + L(-) The reactants are neutral (Nu is a neutral nucleophile, R-L is neutral). The transition state develops charge separation (partial positive on Nu, partial negative on L as the bond breaks/forms). Since the transition state is more polar (charged) than the reactants, increasing solvent polarity stabilizes the transition state more than the ground state, lowering the activation energy. Therefore, increasing solvent polarity increases the rate of reaction A. Answer for A: (a) increases Reaction B: R-L(+) --> R(+) + :L The reactant R-L(+) is a cation (charged, localized on the molecule). The transition state disperses this charge between the developing R(+) and the leaving group L. Since charge is dispersed (delocalized) in the transition state compared to the reactant (which has concentrated charge), increasing solvent polarity stabilizes the reactant more than the transition state. This raises the activation energy and decreases the rate. Answer for B: (b) decreases Why other options fail for A: The rate cannot remain constant or decrease because charge is being created in the TS; more polar solvents stabilize this charged TS. For B: The rate cannot increase because charge is being dispersed, not created; polar solvents favor concentrated charge (reactant) over dispersed charge (TS). Therefore, the correct answer is {"A": ["A"], "B": ["B"]}.