Distribution and conformational change of ethylene glycol by ab initio MD method

Abstract

Ethylene glycol(EG) has two hydroxyl(OH) groups and can make intramolecular hydrogen bond(s), forming various conformers. In this study, we calculated the geometries of local minimum and transition state conformers using the HF/6-31G* and MP2/6-31G* levels of theory. The potential energy maps were made by single point calculations. The distribution of EG conformers at some temperature was obtained by means of ab initio MD calculations starting from two major conformers(tG+g-,tTt) using HF/6-31G*. The ab initio MD method performs ab initio MO calculations at each MD step. In the trajectory at 300K, the OCCO conformational isomerizations have not been observed. At 500K, EG changed its conformation in high energy region, and the OCCO conformational isomerizatons were observed several times. The OCCO conformational isomerizations occurred along the low energy area in potential energy maps at most of the times, while processes of isomerizations were observed via high energy conformations. The difficulty of the OCCO conformational isomerization is due to the high rotational barriers(about 5.4kcal/mol). In addition to those barriers, it is probable that the conformation and the direction of the movement of OH groups are important toward the OCCO conformational isomerizations.