Gauche/trans equilibria of 2,2′-Bi-1,3-dioxepanyl and 2,2′-Bi-1,3-dithiepanyl in different media - Theory and experiment

Abstract

The gauche/trans conformational equilibria of 2,2′-bi-1,3-dioxepanyl 1 and 2,2′-bi-1,3-dithiepanyl 2 dissolved in carbon tetrachloride and benzene are studied through dipole moment determination. Analyses of the relative permittivity data show that both 1 and 2 favor the gauche form at 25°C. However, X-ray crystallographic determination revealed that 1 and 2 favored the trans conformation in the solid state. Ab initio and DFT calculations were performed to examine the structural features of 1 and 2 and study the effects of solvent on these molecules. The calculated gauche/trans equilibria of 1 and 2 in different media are in good agreement with the experimental findings. CH⋯X (X = O or S) interactions are important to understand the structures and relative energies of these 1,3-diheteroane systems.