hydrogen bond A type of electrostatic interaction between electronegative (fluorine, nitrogen, or oxygen) atoms in one molecule and hydrogen atoms bound to electronegative atoms in another molecule. It is a strong dipole–dipole attraction caused by the electron-withdrawing properties of the electronegative atom. Thus, in the water molecule the oxygen atom attracts the electrons in the O–H bonds. The hydrogen atom has no inner shells of electrons to shield the nucleus, and there is an electrostatic interaction between the hydrogen proton and a lone pair of electrons on an oxygen atom in a neighbouring molecule. Each oxygen atom has two lone pairs and can make hydrogen bonds to two different hydrogen atoms. The strengths of hydrogen bonds are about one tenth of the strengths of normal covalent bonds. Hydrogen bonding does, however, have significant effects on physical properties. Thus it accounts for the unusual properties of water and for its relatively high boiling point. It is also of great importance in living organisms. Hydrogen bonding occurs between bases in the chains of DNA (see base pairing). It also occurs between the C=O and N–H groups in proteins, and is responsible for maintaining the secondary structure.

hydrogen bond The force of attraction (the hydrogen force) that exists between polar molecules containing hydrogen atoms, or between one part of a molecular chain and another part that contains bonded hydrogen. It occurs because the single electron in the hydrogen atom is held only weakly, so hydrogen readily forms ionic bonds, which allow a hydrogen atom to link other atoms. Some of the properties of water are due to the hydrogen bond that links water molecules. DNA molecules are linked by hydrogen bonds, and hydrogen bonding is also important in linking other organic molecules. See also COVALENT BOND; IONIC BOND; and METALLIC BOND.

hydrogen bond A bond between molecules in one of which hydrogen atoms are bound to the electronegative atoms fluorine (F), nitrogen (N), or oxygen (O), producing a strongly polarized bond (e.g. O–H) that bonds weakly to another H (e.g. H–O–H, or H₂O). Hydrogen bonding gives water its peculiar properties and provides the link in base pairing. See also covalent bond, ionic bond, and metallic bond.

hydrogen bond The force of attraction (the hydrogen force) that exists between polar molecules containing hydrogen atoms, or between one part of a molecular chain and another part that contains bonded hydrogen. It occurs because the single electron in the hydrogen atom is held only weakly, so hydrogen readily forms ionic bonds, which allow a hydrogen atom to link other atoms. Some of the properties of water are due to the hydrogen bond that links water molecules. DNA molecules are linked by hydrogen bonds, and hydrogen bonding is also important in linking other organic molecules.