The Unimolecular Chemistry of Protonated Glycinamide and the Proton Affinity of Glycinamide—Mass Spectrometric Experiments and Theoretical Model

The potential energy hypersurface of protonated glycinamide (GAH + ) has been investigated experimentally and theoretically. The calculated G2(MP2) value for the proton affinity of glycinamide, PA calcd = 919 kJ mol ‐1 , is in good agreement with the measured value of 908 PA exp <914kJ mol ‐1 . The fact that the amide group is a better hydrogenbond acceptor explains why glycinamide has a higher PA than glycine. Proton transfer experiments with glycinamide performed in a Fourier transform mass spectrometer and analysis of metastable GAH + ions in a four‐sector mass spectrometer show that the lowest‐energy unimolecular reactions are two distinct processes: 1) loss of CO, which has a substantial barrier for the reverse reaction, and 2) loss of CO plus NH 3 , which has no barrier for the reverse reaction. Ab initio quantum chemical calculations give a reaction model that is consistent with the observed fragmentation pattern.