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The Unimolecular Chemistry of Protonated Glycinamide and the Proton Affinity of Glycinamide—Mass Spectrometric Experiments and Theoretical Model
Author(s) -
Uggerud Einar,
Hvistendahl Georg,
Rasmussen Bård,
Kinser Robin D.,
Ridge Douglas P.
Publication year - 1996
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19960020917
Subject(s) - chemistry , proton affinity , protonation , mass spectrometry , ion , proton , fragmentation (computing) , metastability , computational chemistry , analytical chemistry (journal) , organic chemistry , physics , chromatography , quantum mechanics , computer science , operating system
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.