Conformational stability from temperature-dependent FT-IR spectra of liquid rare gas solutions, barriers to internal rotation, vibrational assignment, and ab initio calculations for 3-chloropropene

The infrared spectra of 3-chloropropene, (allyl chloride) CH2=CHCH2Cl, diss olved in liquid argon (94-124 K), liquid krypton (117-167 K), and liquid xe non (161-221 K) at concentrations of about 1 x 10(-2) M are reported. In ar gon the solubility is too low to determine the enthalpy difference between the conformers. For liquid krypton and xenon the temperature dependence of the infrared spectra in the CH2 deformation region has been used to obtain an enthalpy difference of 96 +/- 5 cm(-1) (1.15 +/- 0.06 kJ/mol) for the kr ypton solution and 147 +/- 20 cm(-1) (1.76 +/- 0.24 kJ/mol) for the xenon s olution with the gauche conformer the more stable rotamer. The asymmetric t orsional transitions have been remeasured in the far-infrared spectrum and the fundamental for the cis conformer is observed at 147.3 cm(-1) with four successive hot bands falling to lower frequency and the fundamental for th e gauche conformer is observed at 102 cm(-1) with four accompanying hot ban ds. Utilizing the enthalpy and torsional data along with the gauche dihedra l angle (ClCCC) of 120.0 degrees, the potential function governing the conf ormational interchange has been determined. The cis to gauche, gauche to ga uche, and gauche to cis barriers have been determined to be 881, 699, and 1 005 cm(-1), respectively. The structural parameters, conformational stabili ty, infrared intensities, Raman activities, and depolarization ratios, alon g with the vibrational frequencies, have been obtained from ab initio calcu lations at the MP2/6-31G(d) level. These data are compared to the correspon ding experimental quantities, and the overall results are compared and cont rasted to those for some similar molecules.