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Electrophilicity of 5-Benzylidene-1,3-dimethylbarbituric and -thiobarbituric Acids

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posted on 23.11.2007, 00:00 by Florian Seeliger, Stefan T. A. Berger, Grygoriy Y. Remennikov, Kurt Polborn, Herbert Mayr
The kinetics of reactions of acceptor-stabilized carbanions 2am with benzylidenebarbituric and -thiobarbituric acids 1ae has been determined in a dimethyl sulfoxide solution at 20 °C. Second-order rate constants were employed to determine the electrophilicity parameters E of the benzylidenebarbituric and -thiobarbituric acids 1ae according to the correlation equation log k(20 °C) = s(N + E). With E parameters in the range of −10.4 to −13.9, the electrophilicities of 1ae are comparable to those of analogously substituted benzylidenemalononitriles.