Knowledge Bank

The Raman 3100 to $10cm-1$) and infrared (3100 to $30cm-1$) spectra of trifluoroacetyl isocyanate, $CF3C(O)NCO$, have been recorded for the gas and solid. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. The observed bands are assigned on the basis of the more stable {cis} conformer (isocyanate group {cis} to the carbonyl bond) and the less stable {trans} conformer in all three physical states. The potential function governing conformational interchange has been determined and the values of the potential constants are: $V1=356\pm 14,V2=1865\pm andV3=203\pm 6cm-1$. Variable temperature studies of the Raman spectrum of the liquid gives a $\Delta H$ of $236\pm 30cm-1(675\pm 86$ cal/mol). A complete vibrational assignment is proposed for the {cis} conformer based on infrared band contours, Raman depolarization data, group frequencies, relative intensities, and normal coordinate calculations. Also, several of the fundamentals of the {trans} conformer have been assigned. The experimental conformational stability, barriers to internal rotation, structural parameters, and fundamental vibrational frequencies are compared with those obtained from {ab initio} gradient calculations.