Towards the understanding of the spectroscopic behaviour of the C–H oscillator in C–H⋯O hydrogen bonds: the effect of solvent polarity

The effect of solvent polarity versus specific C–H⋯O contacts on the vibrational νC–H mode is studied using CHCl3 as a model system. Ab initio SCI–PCM calculations show that the overall shift of the νC–H band, sometimes ascribed to the C–H⋯O hydrogen bonding, can in fact be explained by the electrostatic interaction with a dielectric environment. The presence of a new νC–H band – assigned to the C–H⋯O bonded forms – remains as the most reliable evidence of C–H⋯O hydrogen bonding.