Structures and vibrational frequencies of imidazole, benzimidazole and its 2-alkyl derivatives determined by DFT calculations

الملخص EN

The molecular structures of imidazole, benzimidazole and its 2-alkylderivatives as well as their vibrational frequencies have been determined by DFT method using B3LYP theory level at 6-311G (d, p) basis set.

Some physical properties such as total energy, HOMO, LUMO energies and dipole moments of studied molecules were calculated also determined.

2-ethyl derivative posses the lowest energy -458 hartree compare with imidazole -226.27 hartree whereas the smallest energy gap between HOMO and LUMO is in 2-methyl derivative it is the most chemically reactive.

Imidazole and benzimidazole are planar molecules and have dipole moments 3.7285 and 3.5528 D respectively.

C4 atom carries the highest negative charge compare with the C2 atom in imidazole.

In all studied molecules N1 carries higher negative charge than N3, but N1 and N3 atoms show the highest negative charge in 2-ethyl derivative.

The hydrogen atom of N-H group is coplanar in all studied molecules.

Vibration frequencies and simulated spectra have been discussed and compared with the measured spectra.