Which of the following statements are correct for the S _ N 2 reaction of alkyl halides? I. Both the alkyl halide and the nucleophile are involved in the transition state. II. The reaction proceeds with inversion of configuration at the substitution centre. III. The reaction proceeds with retention of configuration at the substitution centre. IV. The order of reactivity of alkyl halides is 3^ > 2^ > 1^ . V. The nucle

Step-by-step solution

Statement I is correct. The S _ N 2 reaction is a concerted, single-step process where the transition state involves both the alkyl halide and the nucleophile. Statement II is correct. The nucleophile attacks from the backside of the leaving group, leading to an inversion of configuration at the substitution centre. Statement III is incorrect. The reaction proceeds with inversion, not retention. Statement IV is incorrect. Due to steric hindrance, the reactivity order of alkyl halides in S _ N 2 reactions is 1^ > 2^