Molecular structures and vibrational spectra of 2-, 3-and 4-ethylpyridines and 2-, 3-and 4-vinylpyridines by density functional theory and ab initio Hartree-Fock calculations

The molecular structures, vibrational frequencies and corresponding vibrational assignments of 2-, 3- and 4-ethyl and vinyl pyridines have been calculated by ab initio Hatree-Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d,p) basis set level. The vibrations for the vinylpyridines were adapted to their C-s symmetries. The calculated frequencies and optimized geometric parameters (bond lengths and bond angles) were seen to be in a well agreement with the experimental data. The comparison of the observed and calculated results also showed that the scaled B3LYP is superior to the scaled HF method for both the vibrational frequencies and the geometric parameters. Infrared intensities and Raman activities have also been reported. In addition, the highest occupied molecular orbital and lowest unoccupied molecular orbital energies of all the compounds have been simulated, and their energy band gaps have been determined.