MP2 study of the gas phase elimination mechanism of some neutral amino acids and their ethyl esters

The mechanisms of the gas phase elimination of N,N-dimethylglycine, picolinic acid, and N-phenylglycine and their ethyl esters have been examined at Möller-Plesset MP2/6-31G (d, p) level of theory. The ethyl esters of these 2-amino carboxylic acids produce the corresponding amino carboxylic acid and ethylene in a rate-determining step. However, the unstable intermediate amino carboxylic acid rapidly decarboxylate to give the corresponding amino compound. These calculations imply a concerted, semi-polar six-membered cyclic transition state type of mechanism for the ethyl esters, and a non-synchronous five-membered cyclic transition state for the amino acids decarboxylation. The present results support previous mechanistic consideration of the elimination of the above-mentioned compounds in the gas phase.