An optically active alkyl halide, specifically -bromopentane, is subjected to a reaction with sodium — Haloalkanes and Haloarenes Chemistry Question
Question
An optically active alkyl halide, specifically $(R)-2$ -bromopentane, is subjected to a reaction with sodium hydrogen sulfide ($NaSH$) dissolved in pure acetone. What is the explicit stereochemical designation and structural relationship of the major product relative to the starting reactant?
💡 Solution & Explanation
The reaction utilizes a strong nucleophile ($SH^-$) in a highly polar aprotic solvent (acetone) operating on a secondary alkyl halide. These precise conditions overwhelmingly favour the $S_N2$ mechanism. The $SH^-$ nucleophile executes a rigorous backside attack on the chiral carbon, displacing the bromide ion in a concerted step. This process forces the spatial arrangement to flip completely (Walden inversion), seamlessly converting the $(R)$ -configuration directly into the $(S)$ -configuration to yield optically pure $(S)-2$ -pentanethiol.