Conformation of Nitrocyclohexane in the Host Lattice of Its Thiourea Adduct

Abstract

The conformation of nitrocyclohexane in its thiourea adduct was investigated by the measurement of infrared absorption spectra in the region of 4000-30cm^-1. For the purpose of making an assignment of infrared absorption bands of nitrocyclohexane in the adduct, calculation of normal vibration of equatorial and axial conformers of nitrocyclohexane was carried out. In the spctrum of the adduct, the bands at 841cm^-1 and 325cm-' assigned to the axial conformer based on the calculation are strong, while those at 215cm^-1 and 505cm^-1 assigned to the equatrial conformer are very weak. On the contrary, in the spectrum of liquid nitrocyclohexane, the bands assigned to the equatorial conformer are stronger than those of the axial conformer. Therefore, the abundance ratio of both conformers in the adduct is different from that in the liquid. Although it was found that the predominant conformer in the adduct is the axial conformer, it is noteworthy that the equatorial conformer was also found to coexist. The cavity shape of the host lattice of the adduct seems to fit for packing the axial conformers. However, it is not the only factor to determine the species of the guest in the host lattice.