Search

Ketene-forming elimination from C4H3(O)CH2C(O)OC6H3-2-X-4-NO2 (1) promoted by R2NH in MeCN has been studied. The reactions produced elimination products and exhibited second-order kinetics with Brönsted β = 0.51, and |βlg| = 0.47-0.53, indicating that the reaction proceeds by the E2 mechanism via an E2-central transition state. Comparison of β, |βlg|, ∆H6≠, and ∆S6≠ values for R2NH-promoted eliminations from ArCH2C(O)OC6H3-2-X-4-NO2 reveals that the transition-state structures for Ar = furyl and thienyl are similar and more symmetrical than that for Ar = Ph. This outcome has been attributed to the greater double bond stabilizing ability of the former than that of the latter. [ABSTRACT FROM AUTHOR]

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 |βlg| values remained nearly the same for all leaving groups and bases. The results can be described by the negligible pxy interaction coefficient, pxy = ∂β/∂p Klg = ∂βlg/∂p KBH ≈ 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. [ABSTRACT FROM AUTHOR]