A particular type of multicenter (three center - four electron) X–H ...Y in which the central hydrogen atom covalently linked to an electronegative atom X (C
...) forms an additional weaker bond with atom Y (N
...) in the direction of its lone electron pair orbital. The energy of hydrogen bonds, which is usually in the range of 3-15 kcal/mol (12-65 kJ/mol), results from the electrostatic interaction and also from the orbital interaction of the antibonding σ*(XH)MO
of the molecule acting as the hydrogen donor and the non-bonding lone electron pair MO
of the hydrogen acceptor molecule.
PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1945 (https://doi.org/10.1351/pac199971101919)