Raman spectra, vibrational assignment, structural parameters and ab initio calculations for ethyl nitrat

Abstract

AbstractRaman spectra (4000–10 cm−1) of gas, liquid and solid ethyl nitrate were recorded. The qualitative depolarization values were obtained from the spectrum of the liquid. A vibrational assignment for the normal modes is proposed based on depolarization values, group frequencies and normal coordinate calculations. The structures for the trans and gauche conformers have been determined from ab initio Hartree‐Fock gradient calculations using the Gaussian‐82 program with both the 3–21G and 6–31G* basis sets. From this calculation at the 6–31G* level, the energy difference between the more stable trans conformer and the higher energy gauche conformers was found to be 474 cm−1 (1.36 kcal mol−1) with a gauche dihedral angle (CCON) of 79°. The trans to gauche and gauche to gauche barriers are 990 cm−1 (2.83 kcal mol−1) and 3152 cm−1 (9.01 kcal mol−1), respectively. Barriers to internal rotation for the CH3 and NO2 groups were also obtained from ab initio calculations. For the trans conformer the values are 1304 cm−1 (3.73 kcal mol−1) and 2702 cm−1 (7.73 kcal mol−1) and for the gauche conformer they are 1161 cm−1 (3.32 kcal mol−1) and 2758 (7.89 kcal mol−1) for the CH3 and NO2 barriers, respectively. Normal coordinate calculations were also performed for both conformers utilizing force fields calculated from the 3–21G basis set which support the vibrational assignments. The results of this investigation are compared with similar data on some corresponding molecules.