AB-INITIO CONFORMATIONAL-ANALYSIS OF ETHYLENE-GLYCOL AND 1,3-PROPANEDIOL

In this study we report the results of an ab initio investigation of the conformational properties of ethylene glycol and 1,3-propanediol. We performed HF/6-31++G** optimizations of the geometries of 10 ethylene glycol conformers, and HF/4-31+G* optimizations of 23 1,3-propanediol conformers. In the case of ethylene glycol we found the lowest energy conformers to have a gauche OCCO arrangement, stabilized by intramolecular hydrogen bonding. In case of 1,3-propanediol the lowest energy conformers have gauche OCCC arrangements. Intramolecular hydrogen bonding also plays an important role in this molecule. In both molecules we found that the ab initio results agree relatively well with available experimental data. It was also found that the conformational trends in the smaller ethylene glycol molecule are maintained in the larger 1,3-propanediol molecule. The introduction of Moller-Plesset second order electron correlation strengthens the intramolecular hydrogen bonding and the gauche-effect in both molecules.