Conformational stability, infrared and Raman spectra, vibrational assignments, and theoretical calculations of cyclohexylamine

•Conformational analysis has been determined between the possible conformers of cyclohexylamine.•Vibrational assignments are given for the molecule.•Ab initio and density functional theory calculations have been carried out for all possible conformers.

The infrared spectra (4000–400 cm−1) of the gas and Raman spectra (4000–50 cm−1) of the liquid have been recorded. Additionally, the variable temperature (−65 to −100 °C) infrared spectra of the sample dissolved in liquefied xenon was recorded from (3800–400 cm−1). The three possible conformers have been identified and their relative stabilities obtained with enthalpy difference relative to trans-Axial (t-Ax) of 58 ± 15 cm−1 for gauche-Equatorial (g-Eq) ⩾ 65 ± 12 cm−1 for trans-Equatorial (t-Eq). The percentage of the three conformers is estimated to be 31% for the t-Ax, 47 ± 2% for g-Eq and 22 ± 1% for t-Eq at ambient temperature. The conformational stabilities have been predicted from theoretical calculations by utilizing several different basis sets up to 6-311+G(2df, 2pd) from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been provided for the observed bands for all three conformers which are predicted by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for all of the conformers. The results are discussed and compared to the corresponding properties of some related molecules.

Graphical abstractTemperature dependent mid-infrared spectrum of cyclohexylamine dissolved in liquefied xenon.Figure optionsDownload full-size imageDownload as PowerPoint slide