Elimination Reactions of (E)-2,4,6-Trinitrobenzaldehyde O-Aryloximes Promoted by R3N/R3NH+ in 70 mol % MeCN(aq). Effect of beta-Aryl Group the Nitrile-Forming Transition-State

Abstract

Nitrile-forming eliminations from (E)-2,4,6-(NO2)(3)C6H2CH=NOC6H4-2-X-4-NO2 (1) promoted by R3NH/R3NH+ in 70 mol % MeCN(aq) have been studied kinetically. When X = NO2, the reactions exhibited secondorder kinetics as well as Bronsted beta = 0.63 and vertical bar beta(lg)vertical bar,1= 0.34-0.46, and an E2 mechanism is evident. As the leaving group was made poorer (X = H, Cl, and CF3), Bronsted beta value increased from 0.63 to 0.85-0.89 without much change in the vertical bar beta(lg)vertical bar value E2, indicating that structure of the transition state changed to an Elcb-like with extensive C beta-H bond cleavage, significant negative charge development at the beta-carbon, and limited C alpha-OAr bond cleavage.