Multiple structure–reactivity relationships for a Menschutkin-type SN2 reaction

Abstract

The mechanisms of nucleophilic displacement was studied by using three variable systems of ρ_X, ρ_Y, and ρ_Z obtained from the change of substituents X, Y, and Z for the reaction of (Z)-substituted benzyl (X)-benzenesulphonates with (Y)-substituted N,N-dimethylanilines in acetone at 35 °C. The coefficient of the interaction term, ρ_XY, has a value of 0.21 which means that bond-making and -breaking are concerted in the S_N2 transition state. In the range Z = H to p-NO₂, in which the S_N2 mechanism is predicted to be dominant, the |ρ_ZY| value is very large, 0.5, which means that the interaction between Z and Y is very large. |ρ_ZX| is ca. 0.06 which means that the interaction is small between X and Z. In contrast, in the range Z = H to p-Me, in which the S_N1 mechanism is dominant, the |ρ_ZY| value is nearly zero, indicating no interaction between Z and Y. Changes of substituent effect and interaction terms, ρ_XY, ρ_YZ, and ρ_ZX are useful tools for distinguishing wrong reaction mechanisms.