Spectra and structure of small ring compounds: Part XXXV. Vibrational spectra and ring-puckering and torsional potential functions of cyclobutylamine

Abstract

The IR spectra (50–4000 cm −1) of gaseous and solid cyclobutylamine and cyclobutylamine-N- d 2 and the Raman spectra (25–4000 cm −1) of gaseous, liquid and solid cyclobutylamine and cyclobutylamine-N- d 2 have been recorded. Depolarization values were measured for both the gaseous and liquid states. Most of the thirty-six fundamental vibrations have been assigned and support for more than one molecular configuration is presented. In the low frequency region for the “light” compound, a series of four Q-branches have been assigned to transitions between energy levels of the ring-puckering vibration for the equatorial isomer. The transitional frequencies were fitted to an asymmetric single-minimum potential function of the form: V(X) = 0.474 × 10 6 X 4 - 0.204 × 10 5 X 2 + 0.993 × 10 5 X 3 with a reduced mass of 160 amu. The following torsional potential constants were determined for the “light” molecule- V 1 = 77.8 ± 17.0 cm −1, V 3 = 784.0 ± 3.3 cm −1. The trans conformation was found to be more stable than the gauche form by approximately 58 cm −1 (0.17 kcal mol −1). The barriers to trans-gauche, gauche-trans, and gauche-gauche interconversion are 803, 745 and 803 cm −1, respectively.