Concerning the Regioselectivity of Gas Phase Reactions of Glycine with Electrophiles. The Cases of the Dimethylchlorinium Ion and the Methoxymethyl Cationl

Abstract

The gas phase reactions of glycine with the dimethylchlorinium ion and the methoxymethyl cation in the Cl source of a tandem mass spectrometer have been investigated. The mechanisms of these reactions were determined by analyzing the unimolecular fragmentation reactions of the product ions. (CH3)2C1+ undergoes a nonregioselective Sn2 reaction, with methylation occurring at both nitrogen and oxygen. This is consistent with the relative methyl cation affinities (MCAs) of CH3CI (MCA (CH3CI) = 62.0 kcal mol-1) and those calculated via ab initio calculations (at the MP2/6-31G*//HF/6-31G* level) for the three nucleophilic sites in glycine: MCA (H2N group) = 116.0 kcal mol-1, MCA (C=0 group) = 90.8..