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Wikipedia A hydrogen bond is the attractive force between one electronegative atom and a hydrogen covalently bonded to another electronegative atom. It results from a dipole-dipole force with a hydrogen atom bonded to nitrogen, oxygen or fluorine (thus the name "hydrogen bond", which must not be confused with a covalent bond to hydrogen). The energy of a hydrogen bond (typically 5 to 30 k. J/mole) is comparable to that of weak covalent bonds (155 k. J/mol), and a typical covalent bond is only 20 times stronger than an intermolecular hydrogen bond.

These bonds can occur between molecules (intermolecularly), or within different parts of a single molecule (intramolecularly). [2] The hydrogen bond is a very strong fixed dipole-dipole van der Waals-Keesom force, but weaker than covalent, ionic and metallic bonds. The hydrogen bond is somewhere between a covalent bond an electrostatic intermolecular attraction. This type of bond occurs in both inorganic molecules (such as water) and organic molecules (such as DNA). Intermolecular hydrogen bonding is responsible for the high boiling point of water (100 °C). This is because of the strong hydrogen bond, as opposed to other group 16 hydrides. Intramolecular hydrogen bonding is partly responsible for the secondary, tertiary, and quaternary structures of proteins and nucleic acids.

Martin Chaplin BSc Ph. D CChem FRSC Professor of Applied Science Water and Aqueous Systems Research Head of the Food Research Centre London South Bank University Borough Road London SE 1 0 AA UK Tel. No. (44) 20 7815 7970 martin. chaplin@lsbu. ac. uk