The Nature of Hydrogen Bonds: A Delineation of the Role of Different Energy Components on Hydrogen Bond Strengths and Lengths.

Hydrogen bonds are a complex interplay between different energy components, and their nature is still subject of an ongoing debate. In this minireview, we therefore provide an overview of the different perspectives on hydrogen bonding. This will be done by discussing the following individual energy components: 1) electrostatic interactions, 2) charge-transfer interactions, 3) π-resonance assistance, 4) steric repulsion, 5) cooperative effects, 6) dispersion interactions and 7) secondary electrostatic interactions. We demonstrate how these energetic factors are essential in a correct description of the hydrogen bond, and discuss several examples of systems whose energetic and geometrical features are not captured by easy-to-use predictive models.