PROTON AND SODIUM-ION AFFINITIES OF GLYCINE AND ITS SODIUM-SALT IN THE GAS-PHASE - ABINITIO CALCULATIONS

被引:95
作者
BOUCHONNET, S
HOPPILLIARD, Y
机构
[1] Laboratoire Dcmr, Ecole Polytechnique, Palaiseau
来源
ORGANIC MASS SPECTROMETRY | 1992年 / 27卷 / 02期
关键词
D O I
10.1002/oms.1210270202
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The energies of protonation and Na+ cationization of glycine (GLY) and its (GLY - H + Na) salt in the gas phase were calculated using ab initio calculations. The proton affinity of GLY, valued at the MP2/6-31G* parallel-to 3-21G level, is 937 kJ mol-1. The amino function is confirmed to be the most favourable site of protonation: 'proton affinities' of the carbonyl and hydroxyl functions are calculated to be 75 and 180 kJ mol-1, respectively, lower than that of NH2 at the MP2/6-31G* parallel-to 3-21G level. Calculations performed up to the MP2/6-31G* parallel-to 3-21G level give the Na+ affinity of GLY as 189 kJ mol-1 and the H+ and Na+ affinities of (GLY - H + Na) as 1079 and 298 kJ mol-1, respectively. The geometries of all neutral and protonated species optimized with the 3-21G basis set are described. Both H+ and Na+ cations complex preferably between the nitrogen atom and the carbonyl oxygen atom, leading to pseudo-five-membered ring structures in which Na-O and Na-N bonds lengths are greater than 2 angstrom.
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页码:71 / 76
页数:6
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