When pure -2-pentanol is subjected to reaction with phosphorus trichloride (), it forms 2-chloropent — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

The reaction of an alcohol with $PCl_3$ follows a bimolecular nucleophilic substitution ($S_N2$) mechanism. The oxygen atom first attacks the phosphorus to form a good leaving group (a phosphite ester intermediate). Then, the displaced chloride ion ($Cl^-$) acts as a nucleophile, attacking the electrophilic carbon from the backside (opposite the leaving group). This concerted backside attack results in complete Walden inversion. Therefore, $(S)$ -2-pentanol strictly yields $(R)$ -2-chloropentane.