NMR spectroscopy and quantum mechanical calculations have been used to investigate the protonation of beta-cyanoenamines. One-dimensional variable-temperature spectroscopy, two-dimensional exchange spectroscopy (2D EXSY), and density functional calculations provide convincing evidence that the favored site of protonation in 1,1-bis(dimethylamino)-2-cyano-2-p-X-phenyl-substituted ethylenes (X = NO2, CF3, Br, F, or CH3) is the nitrogen of the cyano group. This results in the formation of a ketenimine amidinium ion in solution. When X is less electron withdrawing than -NO2, an equilibrium mixture is formed consisting of 60-93% CN-protonated enamine with the remainder protonated at the beta-carbon. Calculational results also support predominantly CN-protonation in these systems. Both experimental and calculational results show no evidence of protonation at the amino nitrogen.