The Gauche-Effect in 1,2-Bis(arylsulfonate)ethanes

With an aim of obtaining a fundamental understanding of C-C bond conformation theory, the molecular structure of an ethane with electron-withdrawing groups, 1,2-bis(4-methoxybenzene-sulfonate)ethane, was elucidated. According to the general conformation rule for alkanes, which states that molecules adopt a stabilized structure to avoid steric repulsion, ethanes typically adopt anti-conformation. However, the title compound exhibited gauche-conformation, as revealed by a single crystal diffraction study. Theoretical studies also support this behavior. Natural Bond Orbital (NBO) analysis suggests that the orbital interaction between the sigma*CO orbital, attributable to the sulfonate groups, and the adjacent sigma CH orbital stabilizes the gauche-conformation. The authors conclude that the sulfonate group acts as a gauche-effect synthon, which is widely applicable in organic chemistry.