Ab Initio Determination of Molecular Geometry and Vibrational Frequencies of Benzotrifluoride

Using Gaussian 05 Revision C.02 version of the quantum chemical program ab initio computations has been carried out to compute optimized geometry, harmonic vibrational frequencies along with intensities in IR and Raman spectra and atomic charges at rhf / 6–31+g*, b3lyp / 6–31++g** and b3lyp / 6–311++g** levels. The optimized molecular structure is found to possess Cs point group symmetry with the plane of symmetry passing through the C atom, to which the CF3 group is attached, the centrally opposite C atom and the C atom of the CF3 group and perpendicular to the phenyl ring plane. One of the three F atoms of the CF3 group is found to be on one side of the ring plane and is situated on the plane of the symmetry while the other two F atoms are found to be on the other side of the ring plane placed symmetrically on either side of the symmetry plane. Vibrational assignments for the normal modes have been reviewed. To make vibrational assignments for the normal modes of vibration the Gauss View software was used. The CF3 group has the characteristic frequencies in the 340, 768, 1072, 1152 and 1318 cm-1 which are due to the modes δs (CF3), Vs (CF3 ), Vas(CF3) (a’), Vas(CF3) (a”) and V(C–CF3 ) respectively. The torsional frequency of the CF3 group is found to be 16 cm-1 which would lead to barrier height of ~ 0.5 kJ / mol for the torsional motion of the CF3 group.