Elimination reactions of (E)-2,4-(NO2)2C 6H2CH=NOC6H3-2-X-4-NO2 (1a-e) promoted by R3N/R3NH+ in 70 mol % MeCN(aq) have been studied kinetically. The reactions are second-order and exhibit Brönsted β = 0.80- 0.84 and |βlg| = 0.39-0.42, respectively. For all leaving groups and bases employed in this study, the β and |βlg| values remained almost the same. The results can be described by a negligible pxy interaction coefficient, pxy = δβ/pKlg = δβlg/pK-azip ̃ 0, which describes the interaction between the base catalyst and the leaving group. The negligible pxy interaction coefficient is consistent with the (E1cb) irr mechanism. Change of the base-solvent system from R 3N/MeCN to R3N/R3NH+-70 mol % MeCN(aq) changed the reaction mechanism from E2 to (E1cb)irr. Noteworthy was the relative insensitivity of the transition state structure to the reaction mechanism change.
- E1cb-like and (E1cb)
- Leaving group and base-solvent effect
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