RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL-ROTATION, AB-INITIO CALCULATIONS AND VIBRATIONAL ASSIGNMENT OF CYANOMETHYL METHYL-ETHER

The Raman spectra (3400-10 cm-1) of gaseous, liquid and solid and the infrared spectra (3500-35 cm-1) of gaseous and solid cyanomethyl methyl ether (methoxyacetonitrile), (CN)CH2OCH3, were recorded. The far-infrared spectrum of the gas was recorded at a resolution of 0.10 cm-1 in the region from 370 to 30 cm-1. The fundamental asymmetric torsions of the gauche and trans conformations were observed at 112.5 and 104.6 cm-1, respectively, with the gauche form having two excited-state transitions falling to lower wavenumber. From these data, along with the enthalpy difference and gauche dihedral angle, the asymmetric torsional potential function was calculated with the following coefficients: V1 = 153 +/- 9, V2 = -619 +/- 8, V3 = 1000 +/- 2 and V4 = -100 +/- 2 cm-1. From this potential function, the trans to gauche, gauche to gauche and gauche to trans barriers were determined as 512, 1592 and 951 cm-1, respectively, with an enthalpy difference of 439 +/- 19 cm-1 (1255 +/- 54 cal mol-1) and the gauche conformer the more stable form in the gas phase. The enthalpy difference was also determined experimentally from variable-temperature studies of the Raman spectrum and a value of 337 +/- 44 cm-1 (964 +/- 126 cal mol-1) was obtained for the liquid with the gauche form more stable. Additionally, the symmetric methyl torsions of both gauche and trans forms were observed at 170.4 and 217.6 cm-1, respectively. On the basis of a one-dimensional model, the barrier to internal rotation of the methyl moiety was determined as 839 cm-1 (2.40 kcal mol-1) for the gauche conformer and 947 cm-1 (2.71 kcal mol-1) for the trans form. A complete vibrational assignment is proposed for a gauche-trans equilibrium in the gas and liquid phases from the Raman (3200-10 cm-1) and infrared (3200-35 cm-1) spectra, but in the solid state only the gauche conformer remains. The structural parameters, conformational stability, barriers to internal rotation and fundamental vibrational frequencies which were determined experimentally were compared with those obtained from ab initio calculations employing the RHF/4-31G*, RHF/6-31G* and MP2/6-31 + + G** basis sets. These results were compared with the corresponding quantities obtained for some similar molecules.