Low frequency vibrational spectra of monosubstituted benzenes in the liquid state

FT-IR, FT-Raman spectra and other molecular properties of 3,5-dichlorobenzonitrile: a DFT study

The IR and Raman spectra of 3,5-dichlorobenzonitrile (3,5-DCBN) molecule were recorded at room temperature and then the assignment of the observed fundamental bands were achieved by the aid of the theoretical vibrational spectral data obtained from a quantum chemical study carried out for the free molecule case. In the calculations performed to determine the molecular geometry, vibrational spectral data and thermodynamic parameters, Møller-Plesset second order perturbation theory (MP2) and hybrid Density Functional Theory (DFT) types of electronic structure methods, B3LYP and B3PW91, were used. The overestimations of the calculated harmonic wavenumbers were efficiently corrected by the aid of a specific scaling procedure. This empirical scaling process significantly increased the reliability of our assignments and analyses on the observed bands due to different vibrational normal modes of the molecule. For the majority of the normal modes, the deviations between the corresponding experimental and scaled theoretical wavenumbers have located in the expected range. A correct characterization of the normal modes is of vital importance in the assignment of the observed bands, and this was successfully done by the aid of the Potential Energy Distributions (PEDs) separately calculated for each normal mode of 3,5-DCBN.

Vibrational spectroscopic, molecular structure, first hyperpolarizability and NBO studies of 4'-methylbiphenyl-2-carbonitrile

The FT-IR, FT-Raman spectra and XRD of 4'-methylbiphenyl-2-carbonitrile were recorded and analyzed. The frequencies were computed at various density functional theoretical levels using Gaussian09 software package. The data obtained from theoretical calculations were used to assign vibrational bands obtained in infrared and Raman spectra of the studied molecule. Potential energy distribution of the normal modes of vibrations were done using GAR2PED program. The geometrical parameters of the title compound are in agreement with XRD crystal structure data. The first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non linear optics. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. According to XRD data, the dihedral angles between the mean planes of the two benzene rings is 44.7° and the crystal packing is stabilized by weak intermolecular π-π stacking interactions.