Dihydrogen bond and X–H…σ interaction as sub‐classes of hydrogen bond

Dihydrogen bond (DHB) and X–H…σ interaction are discussed and compared here. Both interactions possess numerous characteristics of the hydrogen bond (HB). The Natural Bond Orbitals method results show that σ → σ* is the most important interaction connected with the electron charge transfer from the Lewis base to the Lewis acid for the DHB as well as for the X–H…σ HB. However, there are distinct differences between these interactions, and this is evident from the analysis based on the Quantum Theory of Atoms in Molecules as well as from the decomposition of the energy of interaction. The X–H…π interaction is also discussed here since it possesses few characteristics typical for the X–H…σ interaction and not for the DHB.