Vibrational spectroscopic investigation (FT-IR and FT-Raman) on 1,2-dibromobenzene by HF and hybrid (LSDA and B3LYP) calculations.

The FT-IR and FT-Raman spectra of the compound 1,2-dibromobenzene have been recorded in the region 4000-100cm(-1). The vibrational analysis has been made using HF and DFT (B3LYP and LSDA) level of theory by employing 6-31 +G (d, p) and 6-311 ++G (d, p) basis sets. Optimized geometrical parameters have been calculated, interpreted and compared with the reported experimental values of some halogen-substituted benzene. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction of HF and DFT. The geometrical structure of the compound is fractured by the substitutions of couple of Br in the ring. From the vibrational assignments it is observed that, the vibrational pattern of the fundamental modes is realigned slightly with respect to the substitutions. The simulated FT-IR and FT-Raman spectra of the compound for different methods are compared with the experimental spectra. The impact of Br in the vibrational assignments of the molecule is also investigated.

Molecular structure and vibrational analysis of 3-Ethylpyridine using ab initio HF and density functional theory (B3LYP) calculations.

The FT-Raman and FT-IR spectra for 3-Ethylpyridine (3-EP) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using HF/DFT (B3LYP) method by employing 6-31G(d,p) and 6-311++G(d,p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by HF and DFT (B3LYP) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values of some substituted benzene. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from HF and DFT. The scaled vibrational frequencies at B3LYP/6-311++G(d,p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the pyridine are effected upon profusely with the C2H5 substitutions in comparison to pyridine and these differences are interpreted.