Consider the following two reactions involving optically active substrates: Reaction A : (R) -2-bromobutane is treated with NaCN in DMF . Reaction B : (S) -3-bromo-3-methylhexane is treated with H ₂ O . What are the predominant stereochemical outcomes for the products in Reaction A and Reaction B, respectively?

Step-by-step solution

Reaction A involves a secondary alkyl halide reacting with a strong nucleophile ( CN ⁻ ) in a polar aprotic solvent ( DMF ). These conditions strongly favor the S _ N 2 mechanism, which proceeds with complete inversion of configuration. Reaction B involves a tertiary alkyl halide reacting with a weak nucleophile which also acts as a polar protic solvent ( H ₂ O ). These conditions favor the S _ N 1 mechanism, which proceeds via a planar carbocation intermediate, leading to racemization. Answer: Inversion of configu