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

摘要

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