The site of protonation of bifunctional bases with competing basic centers .1. Aromatic nitriles

The experimental values of the gas-phase proton affinities for a variety of 4-substituted benzonitriles, 4-substituted N,N-dimethylanilines, and 4-substituted benzaldehydes have been examined by means of correlation analysis techniques and by ab initio quantum mechanical methods (MP2/6-31G(d) level). From this study it is concluded that in the gas phase, 4-(dimethylamino)benzonitrile essentially protonates on the dimethylamino group, while protonated 4-cyanobenzaldehyde is very nearly a 2:1 mixture of the carbonyl- and cyano-protonated forms.