Hydrogen‐bonded complexes of sulfonamides and thioamides with DMF: FT‐IR and DFT study, NBO analysis

The structure of H-complexes of dimethylformamide (DMF) with N-(2,2,2-trichloro-1-hydroxyethyl)-p-toluenesulfonamide (1), N-[1-(4-chlorophenylsulfonylamino)-2,2,2-trichloro)ethyl]dithiooxamide (2), N,N'-bis[2,2-dichloro-1-(4-chlorophenylsulfonylamino)-2-phenylethyl]ethanebis(thioamide) (3) and N,N'-bis[2,2,2-trichloro-1-(phenylsulfonylamino)ethyl]ethanebis(thioamide) (3a) as proton donors was investigated using Fourier transform infrared spectroscopy and Density Functional Theory calculations. According to calculations, the interaction of DMF with the sulfonamide and thioamide NH groups in the complexes strongly affects the intramolecular H-bonding in 1–3. From the natural bond orbital analysis, complexation with DMF strongly decreases the energy of the intramolecular N−H · · · S = C bonds, up to their rupture. Variation of the strength of the intra- and intermolecular H-bonds in the complexes is consistent with the calculated frequencies of the NH and OH stretching vibrations, and the analysis of the corresponding bands in the IR spectra allows to suggest the preferable structure of the formed H-complexes. Copyright © 2013 John Wiley & Sons, Ltd.