Are non-linear C–H⋯O contacts hydrogen bonds or Van der Waals interactions?: Establishing the limits between hydrogen bonds and Van der Waals interactions

The hydrogen bond nature of angular C–H⋯O contacts is examined to determine when these contacts are better classified as hydrogen bonds or as Van der Waals bonds. To classify the bond we propose to look at the nature of the intermolecular bond critical point present in the electron density of the complex containing the bond. The physics behind this approach is explained using a qualitative orbital overlap model aimed at describing the main changes in the electronic density of the complex produced by the C–H⋯O bending.