Internal rotation in 1,2-di-( p-XC 6H 4)ethanes (X=H, Br, NO 2): infrared spectra and compensation effect

Infrared absorption spectra and internal rotation of 1,2-di-( p-XC 6H 4)ethanes (X=H, Br, NO 2) in crystalline phase, liquid and solutions at various temperatures have been investigated. Band fitting was applied to conformationally sensitive regions of the spectra, and assignment of the peaks to trans and gauche conformations was performed. Enthalpy and entropy differences of the conformers (Δ H 0 and Δ S 0) were found to be solvent-dependent, and it is interpreted in terms of previously discovered compensation effect. The values Δ H 0 and Δ S 0 for 1,2-di-( p-NO 2C 6H 4)ethane obtained are unusually large.