Computational study of the CH···S interaction in a dimer to assess its eventual hydrogen bond character

Abstract

The traditional view of H-bonding has been questioned over the past years, according to new experimental and theoretical evidence pointing to a much more general type of interaction. Recent IUPAC recommendations on H-bonding characterization highlight that a wide range of atoms and molecular fragments may be involved in H-bonding. In this study the H-bond character of a CH···S contact between a methyl group and a sulphur atom from a thioether was assessed. These atoms come in contact in the dimerization of a trityl radical. Several criteria for identifying H-bonds were studied. These include structuralenergetic, spectroscopic (IR and NMR spectroscopies) and theoretical (AIM analysis of the electron density) considerations, which were studied using a computational approach. A medium-quality computational model was used, whose validity was assessed by first studying the mentioned interaction in the CH4···SH2 model complex and comparing the results to those reported in an analogous study by Rovira and Novoa. The chosen computational model describes well the geometries of the complex, although it fails to describe quantitatively the stabilization energy. When studying the criteria reported by the IUPAC, the chosen computational model gives a qualitatively correct description of the CH···S contact in the CH4···SH2 complex, confirming the presence of a weak H-bond, as reported in other studies. For the CH···S contact in the trityl radical dimer a weak blue-shifting H-bond is confirmed between the indicated atoms. The interaction lays in the limit of weak H-bonding and van der Waals interactions.