page_title: Hydrogen bond
section_title: Hydrogen bonds in small molecules
hierarchical_section_title: Hydrogen bond / Hydrogen bonds in small molecules
caption_attribution_description: English: Crystal structure of hexagonal ice (Ih) Русский: Кристаллическая структура гексагонального льда Ih
context_page_description: A hydrogen bond is a partial intermolecular bonding interaction between a lone pair on an electron rich donor atom, particularly the second-row elements nitrogen, oxygen, or fluorine, and the antibonding molecular orbital of a bond between hydrogen and a more electronegative atom or group. Such an interacting system is generally denoted Dn–H···Ac, where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The use of three centered dots for the hydrogen bond is specifically recommended by the IUPAC. While hydrogen bonding has both covalent and electrostatic contributions, and the degrees to which they contribute are currently debated, the present evidence strongly implies that the primary contribution is covalent.
  Hydrogen bonds can be intermolecular or intramolecular. Depending on the nature of the donor and acceptor atoms which constitute the bond, their geometry, and environment, the energy of a hydrogen bond can vary between 1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals interaction, and weaker than fully covalent or ionic bonds.
caption: Crystal structure of hexagonal ice. Gray dashed lines indicate hydrogen bonds