An experimental and theoretical,study of the preferred hydrogen bonding site of methyl isothiocyanate

The hydrogen-bond acceptor properties of MeN=C=S were investigated in vacuo with theoretical (MP2 and DFT) calculations, in CCl4 and (CF3)(2)CHOH solutions by Fourier transform infrared spectrometry and in the solid state through the Cambridge Structural Database. These methods show that MeNCS is a sulfur base in hydrogen bonding., The electrostatic potential at the molecular surface is more negative by 36 kJ mol(-1) around S than around N. The hydrogen bonding of HF is more favorable to sulfur than to nitrogen by ca 5, 4 and 7 kJ mol(-1) respectively, on the dissociation energy, enthalpy and Gibbs energy scales (B3LYP calculations). The selectivity of hydrogen bonding sites appears to be governed by a push-pull mechanism (electrons going from N to S) rather than by hardness. Towards a phenol, the order of sulfur basicity is N=C=S < - S - < S= Cdrop< SPdrop. Copyright (C) 2003 John Wiley Sons, Ltd.