Molecular Structure and Vibrational Spectroscopic Investigation of Secnidazole Using Density Functional Theory

Secnidazole (alpha,2-dimethyl-5-nitro-1H-imidazole-1-ethanol) is an antimicrobical drug, and it is particularly effective in the treatment of amebiasis, giardiasis, trichomoniasis, and bacterial vaginosis. Secnidazole crystallizes as a hernihydrate, which belongs to a monoclinic system having space group P2(1)/c, with a = 12.424 angstrom, b = 12.187 angstrom, c = 6.662 angstrom, and beta = 100.9 degrees. The optimized geometries and total energies of different conformers of the secnidazole molecule have been determined by the method of density functional theory (DFT). For both geometry and total energy, it has been combined with B3LYP functionals having extended basis sets 4-31G, 6-31G, and 6-311++G(d,p) for each of the three stable conformers of secnidazole. Using this optimized structure, we have calculated the infrared and Raman wavenumbers and compared them with the experimental data. The calculated wavenumbers are in an excellent agreement with the experimental values. Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of the most stable conformer of secnidazole. A complete assignment is provided for the observed Raman and IR spectra.