r0 Structural parameters, conformational, vibrational studies and ab initio calculations of cyanocyclopentane

The infrared and Raman spectra (3100-50 cm(-1)) of the gas, liquid or solution, and solid have been recorded of cyanocyclopentane, c-C5H9CN. Variable temperature (-60 to -100 degrees C) studies of the infrared spectra (3100-400 cm(-1)) of the sample dissolved in liquid xenon have been carried out. From these data, both the envelope-equatorial (Eq) and Ax conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 55 +/- 12 cm(-1) (0.66 +/- 0.14 kJ/mol) with the Eq conformer the more stable form. The percentage of the Ax conformer is estimated to be 45 +/- 1% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations by utilizing several different basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been made for the observed bands for both conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The r(0) structural parameter values for the Eq[Ax] form are; for the heavy atom distances (angstrom): C N = 1.160 [1.160] (3); C-alpha-C = 1.463 [1.463] (3); C-alpha-C-beta, C-beta' = 1.543 [1.545] (3); C-beta-C-gamma, C-gamma' = 1.540 [1.541] (3); C-gamma-C-gamma = 1.552 [1.553] (3) and angles (degrees): = angle C alpha-C N = 179.0 [178.9] (5); angle C beta C alpha-C = 113.1 [110.1] (5); angle C beta C alpha C beta' = 103.0 [102.1] (5); angle C alpha C beta C gamma = 104.1 [104.8] (5); angle C beta C gamma C gamma' = 106.3 [106.0] (5). The results are discussed and compared to the corresponding properties of some related molecules. (C) 2015 Elsevier B.V. All rights reserved.