Ab initio Hartree-Fock and density functional theory study on molecular structures, energies, and vibrational frequencies of conformations of 2-hydroxy-3-nitropyridine and 3-hydroxy-2-nitropyridine.

The optimized molecular structures, vibrational frequencies and corresponding vibrational assignments of conformations of 2-hydroxy-3-nitropyridine and 3-hydroxy-2-nitropyridine molecules have been investigated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d,p) basis set. The comparison of the experimental and calculated spectra of the molecules have shown that they exist in two conformations with the two OH bond angles (110 degrees and 250 degrees ) respective to the CO bond in the ground state and their energy curves having two minimums have been drawn.

Molecular structures and vibrational frequencies of xanthine and its methyl derivatives (caffeine and theobromine) by ab initio Hartree-Fock and density functional theory calculations.

The molecular structures, vibrational frequencies and corresponding vibrational assignments of xanthine and its methyl derivatives (caffeine and theobromine) have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-31G(d, p) basis set level. The calculations were utilized to the C(S) symmetries of the molecules. The obtained vibrational frequencies and optimised geometric parameters (bond lengths and bond angles) were seen to be well agreement with the experimental data. The used scale factors which have been obtained the ratio of the frequency values of the strongest peaks in the calculated and experimental spectra seem to cause the gained vibrations well corresponding to the experimental ones. Theoretical infrared intensities and Raman activities are also reported.

Molecular structures and vibrational frequencies of 2-, 3- and 4-pyridine carboxaldehydes by ab initio Hartree-Fock and density functional theory calculations.

The optimised molecular structures, vibrational frequencies and corresponding vibrational assignments of the cis and trans conformers of 2-, 3- and 4-pyridine carboxaldehydes have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d, p) basis set. The calculations were adapted to the C(S) symmetries of all the molecules. The mean vibrational deviations between the vibrational frequency values of the two conformers of all the compounds have been seen to increase while the relative energies increase and it was concluded the more different the molecular structure of the two conformers is the higher the relative energy is between them, and thus a bigger mean vibrational deviation.