Oxygen-by-Sulfur Substitution in CH3OCH2CH2OH: An Ab Initio Comparative Study of Conformational Effects and Intramolecular Interactions

Abstract

Conformational energies, structural parameters and vibrational frequencies for the tgg’, ggg’, ttg, and ttt conformers of CH~XCH~CHZY(XH, Y = 0, S) have been determined by MO ab initio calculations at the MP2/6-31G* level. The results show that the relative strength of the intramolecular X. *HY interaction in tgg’ and ggg‘ conformers diminishes gradually along the series of molecules (0,O) - (0,s) - (S,O) - (S,S), as the X* * *HY contact distance increases by ca. 2 x 10 pm for each of these substitutions. For the (0,O) and (0,s) molecules, the CX-CC trans form is favored over the gauche arrangement, whereas for the (S,O) and ( S , S ) molecules, the gauche conformation is more stable. In addition, the oxygen-by-sulfur substitution in the YH bond increases the relative stability of the CC-YH gauche form with respect to the trans arrangement. In turn, gauche,gauche’ arrangements for the XC-CY and CC-YH axes, respectively, lead to closing of intramolecular rings through X. SHY attractive interactions, hence contributing to improve the stability of the conformations with those dihedral arrangements.