A theoretical study on the decomposition mechanisms of deprotonated glycolic acid

Theoretical calculations at B3LYP and CCSD(T) levels have been performed on the decomposition mechanisms of glycolate. Two new pathways for H2 elimination were identified. The first one proceeds through a concerted mechanism which involves the loss of a α-hydrogen along with the hydroxyl hydrogen. The second pathway involves the step-wise loss of the two α-hydrogen atoms. The previously proposed mechanism initiated by nucleophilic attack proved to be not involved in the H2 elimination pathway. Two previously proposed pathways for CO elimination from glycolate proceeds through nucleophlic attack of the carboxylic oxygen on the α-carbon and through hydrogen transfers were confirmed by our theoretical calculations. The pathway leading to the CH2O elimination from glycolate was found to be branched from the intermediate formed after the nucleophlic attack. The identified pathways and calculated energy barriers well rationalized the experimentally observed fragment ions and their relative peak intensities of mass spectrums.