Electrophilicities of 1,2-Disubstituted Ethylenes

The kinetics of the reactions of maleic anhydride, N-methylmaleimide, fumaronitrile, diethyl fumarate, and diethyl maleate with pyridinium and sulfonium ylides were studied in DMSO at 20 degrees C. All of the reactions were found to follow a second-order rate law, and can be described by the linear free energy relationship logk(2) (20 degrees C) = s(N)(N + E), where N and s(N) are solvent-dependent nucleophile-specific parameters, and E is an electrophile-specific parameter. The electrophilicity parameters E of the investigated acceptor-substituted alkenes were derived from the linear correlations of (logk(2))/s(N) vs. N, and range from -19.8 to -11.1.