Knowledge Bank

The infrared and Raman spectra (3200 to 50 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) of the gas, liquid or solution, and solid have been recorded of isocyanocyclopentane, -C$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">9</mrow>}$NC. FT-microwave studies have also been carried out and 23 transitions were recorded for the envelope-axial (Ax) conformer. Variable temperature (-55 to -100C) studies of the infrared spectra (3200 to 400 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) dissolved in liquid xenon have been carried out. From these data, both the Ax and envelope-equatorial (Eq) conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 102 \pm 10 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ (1.21 \pm 0.03 kJ mol$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) with the Ax conformer the more stable form. The percentage of the Eq conformer is estimated to be 38 $\pm$ 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 heavy atom distances ($\backslash AA$): C$\equiv$N = 1.176 ; C$\mathrm{<mrow\; data-mjx-texclass="ORD">\backslash apha</mrow>}$-N$\equiv$C= 1.432; C$\mathrm{<mrow\; data-mjx-texclass="ORD">\backslash apha</mrow>}$-C,C = 1.534; C-C, C = 1.542; C-C = 1.554 and angles ():$\angle$C$\mathrm{<mrow\; data-mjx-texclass="ORD">\backslash apha</mrow>}$-N\equivC = 177.8; $\angle$CC$\mathrm{<mrow\; data-mjx-texclass="ORD">\backslash apha</mrow>}$-N\equivC = 110.4; $\angle$CC$\mathrm{<mrow\; data-mjx-texclass="ORD">\backslash apha</mrow>}$C= 102.9; $\angle$C$\mathrm{<mrow\; data-mjx-texclass="ORD">\backslash apha</mrow>}$CC = 103.6; $\angle$CCC = 105.9. The results are discussed and compared to the corresponding properties of some related molecules.