The nitro anomaly and Bronsted βnuc values in SN2 reactions on chlorine

The kinetics of chlorine transfer reactions between N-chlorosuccinimide (NCS) and four carbon nucleophiles (the conjugated bases of phenyldinitromethane, Meldrum's acid, phenylmalononitrile and phenylnitromethane) in water were determined. A plot of log k for the S(N)2 reactions vs the pK(a) of the first three conjugated acids of the nucleophiles gave a straight line with a slope (beta(nuc)) of 1.8. The data point for the mononitro derivative, phenylnitromethane, deviates negatively from the line by 6.7 log units. This deviation is typical of proton transfer reactions and was recently shown to occur also in S(N)2 reactions on bromine. Copyright (C) 2002 John Wiley Sons, Ltd.