Proton Affinities and the Site of Protonation of Enamines in the Gas Phase

Article abstract of DOI:10.1021/ja00408a017

The gas-phase proton affinities of a number of methyl-substituted enamines and imines have been measured using ion cyclotron resonance spectroscopy.Comparison of the effect of substituents on the proton affinities of the enamines with those of corresponding amines is used to show that protonation in the gas phase occurs at carbon leading to the formation of an iminium ion.The observation of a large substituent effect for substitution of an α-methyl group also suggests that there is a significant amount of delocalization of positive charge in the iminium ion.A comparison with solution-phase basicities of enamines is also presented.