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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 26, Number 7
BKCSDE 26(7)
July 20, 2005 

Base-Promoted, Ketene-Forming Elimination Reactions. Mechanistic Borderline between E2 and E1cb Mechanisms
Sang Yong Pyun, Bong Rae Cho*
Elimination reactions, Mechanistic borderline, E2 and E1cb mechanisms
Elimination reactions of XC6H4CH2CO2C6H3-2-Y-4-NO2 have been studied under various conditions. When X was moderately electron-withdrawing, Y = H, and base-solvent was R2NH-MeCN, the reaction proceeded by the E2 mechanism via an E1cb-like transition state. Concave downward curve was noted in the Hammett plots. When X = 4-NO2, Y = Cl, CF3, NO2, and the base-solvent was R2NH/R2NH2+ in 70 mol % MeCN(aq), the reaction proceeded by the E2 mechanism. The mechanism changed to a competing E2 and E1cb when X = 4-NO2 and Y = H, MeO, and to the E1cb when X = 2,4-(NO2)2, and Y = NO2. From these results, a plausible pathway of the change of the mechanism from E2 to the E1cb extreme is proposed.
1017 - 1024
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