Elimination reactions of (E)-2,4,6-(NO2)3C6H2CH=NOC(O)C6H4X (3) promoted by R2NH/R2NH2+ in 70 mol% MeCN (aq) have been studied. The reactions produced elimination products and exhibited second-order kinetics. The β and |β1g| values remained nearly the same for all leaving groups and bases. The results can be described by the negligible pxy interaction coefficient, pxy = ∂β/∂pKlg = ∂βlg/∂pKBH ≈ 0, which provides a strong support for the (E1cb)irr mechanism. For eliminations from (E)-ArCH NOC=(O)C6H4X (1, 3) and (E)-2,4,6-(NO2)3C6H2CH=NOAr′ (2, 3), the change of the β-aryl group (Ar) from 2,4-dinitrophenyl (1) to 2,4,6-trinitrophenyl (3) increased the rate by 270-fold without appreciable change in the transition state structure. On the other hand, the leaving group (OAr′) variation from benzoate (3) to 4-nitrophenoxy (2) induced a change in reaction mechanism from (E1cb)irr to E2. These results have been attributed to the cyclic transition state for the nitrile-forming eliminations involving the benzoate leaving group.
- E2 and (E1cb)
- β-aryl group and leaving group effect
ASJC Scopus subject areas