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(+)) h as 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(e xp) < 914 kJ mol(-1). The fact that the amide group is a better hydrog en-bond 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 unimolecul ar reactions are two distinct processes: 1) loss of CO, which has a su bstantial barrier for the reverse reaction, and 2) loss of CO plus NH3 , which has no barrier for the reverse reaction. Ab initio quantum che mical calculations give a reaction model that is consistent with the o bserved fragmentation pattern.