The Conformation and Vibrational Spectra of 1-Cyano-3-Butyne

Abstract

Abstract The infrared spectra of 1-cyano-3-butyne were recorded in the region 4000-50 cm-1 in the vapour and liquid states, as an amorphous and as two different crystalline solids at 90 K. In addition the compound was studied as a high pressure crystalline solid at ambient temperature. Raman spectra of the liquid, including polarization measurements, and of the amorphous and the two crystalline solids at 90 K, were obtained. The spectra revealed the existence of two conformers, anti (Cs) and gauche (C1 symmetry) in the vapour, liquid and in the amorphous solid. When annealed to ca. 140 K a metastable crystal containing one conformer (probably the gauche) was formed, when annealed to ca. 190 K a stable crystal was obtained having the other conformer (probably the anti). The latter conformer was present in the high pressure crystal. Very accurate spectral data for each conformer were collected from the two crystalline solids, making complete assignments for the anti and gauche conformers feasible. The assignments were checked by a normal coordinate analysis. A simple diagonal force field was derived in which the same force constants were employed for the anti and gauche conformers. The mean amplitudes of vibration were calculated for both conformers.