An optically active alcohol, -octan-2-ol, with a specific rotation , is reacted with an excess of in — Haloalkanes and Haloarenes Chemistry Question
Question
An optically active alcohol, $(R)$ -octan-2-ol, with a specific rotation $[\alpha]_D = -10.3^\circ$, is reacted with an excess of $SOCl_2$ in an inert solvent like dioxane (without pyridine). Upon isolation, the resulting 2-chlorooctane is examined in a polarimeter. Which of the following precisely describes its stereochemical profile?
💡 Solution & Explanation
When an alcohol reacts with $SOCl_2$ in the absence of a base (like pyridine), the reaction mechanism is $S_Ni$ (Substitution Nucleophilic internal). An alkyl chlorosulphite intermediate forms and then decomposes. The breaking of the $C-O$ bond and the making of the $C-Cl$ bond occur on the exact same face of the chiral carbon via an intimate ion pair or a cyclic transition state. This front-face delivery ensures that the spatial arrangement remains unchanged, strictly resulting in the retention of configuration ($(R)$ -to- $(R)$). Note: Specific rotation values differ between distinct chemicals, so the exact number will change, but the configuration is retained.