Using¹¹C/¹⁴C Incoming Group and Secondary α-Deuterium KIEs To Determine How a Change in Leaving Group Alters the Structure of the Transition State of the S_N2 Reactions betweenm-Chlorobenzylpara-Substituted Benzenesulfonates and Cyanide Ion

The C-11/C-14 incoming group and secondary alpha-deuterium KIEs and Hammett rho value found by changing the substituent in the leaving group of the S(N)2 reactions between meta-chlorobenzyl para-substituted benzenesulfonates and cyanide ion in 0.5% aqueous acetonitrile at 0 degrees C suggest that these reactions occur via an unsymmetrical, product-like transition state. Changing to a better leaving group leads to a transition state with a slightly shorter nucleophile-alpha-carbon bond and a longer alpha-carbon-leaving group bond. The changes in transition state structure are consistent with the Bond Strength Hypothesis.