DFT studies of molecular structures conformers and vibrational characteristics of sulfanilamide

ESP and MEP plots for conformer I and calculated Raman and IR Spectra of Sulfanilamide conformers. [Display omitted] •Four conformers of sulfanilamide were found to exist.•Out of 51 modes, 26 modes were found to be conformer dependent.•The torsional mode of the sulfonamide NH2 group shows a large variation due to intra-molecular O⋯H bonding.•The sites of the nucleophilic attack are in proximity of the sulfonamide H atoms. Molecular structures and vibrational parameters for all the four possible conformers of sulfanilamide were studied using Gaussian 09 software and PEDs were calculated using GAR2PED software. MEP and HOMO-LUMO energies were computed and NBO analysis was carried out. Optimized geometries possess Cs symmetry. Out of 51 normal modes, 26 modes are conformer sensitive, out of which 2 modes show frequency variation above 75 cm−1 in going from one conformer to another. Out of the 6 internal modes of NH2, 4 modes were found at lower frequencies for S-NH2 group compared to C-NH2 group, due to presence of intra-molecular O⋯H bonds in the SO2(NH2) group. Strength of nucleophilic attack is stronger with the H atoms of C-NH2 group compared to the H atoms of the S-NH2 group. Intra-molecular O⋯H bonds also lead to difference in corresponding geometrical parameters of S-NH2 and C-NH2 groups and difference in atomic charges at corresponding sites.