Raman and infrared spectra, conformational stability, normal coordinate analysis, vibrational assignment, and ab initio calculations of trans-3-pentenenitrile

The Raman (3200-20 cm(-1)) spectra of liquid and solid trans-CH3CH=CHCH2CN, and the infrared (3200-30 cm(-1)) spectra of gaseous and solid trans-3-pen tenenitrile have been recorded. The spectra of the fluid phases are consist ent with two stable conformers in equilibrium at ambient temperature. The m id-infrared spectra of the sample dissolved in liquid xenon as a function o f temperature (- 100 to -55 degreesC) have been recorded. Utilizing two con former pairs, the enthalpy difference has been determined to be 205 +/- 7 c m(-1) (2.45 +/- 0.08 kJ/mol) with the syn conformer being the more stable f orm. Vibrational assignments For the 33 normal modes for the syn conformer and several of those for the gauche form are proposed. The structural param eters, dipole moments, conformational stability, and vibrational frequencie s have been determined from ab initio calculations. The predicted conformat ional stability is consistent with the experimental results. These experime ntal and theoretical results are compared to the corresponding quantities o f some similar molecules. (C) 2000 Elsevier Science B.V. All rights reserve d.