Far-infrared spectra and barriers to internal rotation of ethyl nitrate

Abstract

The far-infrared spectra of gaseous and solid ethyl nitrate, CH 3CH 2ONO 2, have been recorded from 500 to 50 cm −1. The fundamental asymmetric torsion of the trans conformer which has a heavy atom plane has been observed at 112.50 cm −1 with two excited states failing to lower frequencies, and the corresponding fundamental torsion of the gauche conformer was observed at 109.62 cm −1 with two excited states also falling to lower frequencies. The results of a variable temperature Raman study indicate that the trans conformer is more stable than the gauche conformer by 328 ± 96 cm −1 (938 ± 275 cal mol −1). An asymmetric potential function governing the internal rotation about the CH 2O bond is reported which gives a trans to gauche barrier of 894 ± 15 cm −1 (2.56 ± 0.04 kcal mol −1) and a gauche to gauche barrier of 3063 ± 68 cm −1 (8.76 ± 0.20 kcal mol −1) with the trans conformer more stable by 220 ± 148 cm −1 (0.63 ± 0.42 kcal mol −1). Transitions arising from the symmetric CH 3 and NO 2 torsions are observed for both conformers, from which the threefold and twofold periodic barriers to internal rotation have been calculated. For the trans conformer the values are 1002 cm −1 (2.87 kcal mol −1) and 2355 ± 145 cm −1 (6.73 ± 0.42 kcal mol −1) and for the gauche conformer they are 981 cm −1 (2.81 kcal mol −1) and 2736 ± 632 cm −1 (7.82 ± 1.81 kcal mol −1) for the CH 3 and NO 2 rotors, respectively. These results are compared to the corresponding quantities for some similar molecules.