The hydrogen bond is a wondrous thing. It helps give snowflakes their hexagonal symmetry; binds DNA into a double helix; shapes the three-dimensional forms of proteins; and even raises water's boiling point high enough to make a decent cup of tea. [1]
3 November 2010
http://www.rsc.org/chemistryworld/News/2010/November/03111001.asp
The world authority on chemical nomenclature is preparing to scrap the familiar hydrogen bond definition, in light of recent evidence about its true nature. The International Union of Pure and Applied Chemistry's (Iupac's) Physical and Biophysical Chemistry Division has now published its proposal for the revised definition, and the chemical community has until the end of March 2011 to respond. Barring significant objections, it will be adopted shortly thereafter.
Two key factors are motivating the bonding interaction's redefinition. One is a shift in the traditional view that a hydrogen bond is a purely electrostatic attraction between dipoles or charges on a hydrogen and another, electronegative, atom. Elangannan Arunan, who co-chairs the Iupac group assigned to categorise hydrogen bonds and other intermolecular interactions, highlights that there is a variety of evidence, including nuclear magnetic resonance data, that some electron density is shared between them. 'This shows that the hydrogen bond has a covalent nature,' he says.
The current classification also concentrates on fluorine, oxygen and nitrogen, which Arunan says research has been shown as too simplistic. 'Most existing definitions insist hydrogen is connected to the most electronegative atoms,' he tells Chemistry World. 'That is far from complete now.' Arunan points out that Richard Nelmes at the University of Edinburgh, UK discovered that solid hydrogen sulfide has a hydrogen bonding structure resembling ice. 'That's what really shocked chemists,' he says. ...
http://www.rsc.org/chemistryworld/News/2010/November/03111001.asp
The world authority on chemical nomenclature is preparing to scrap the familiar hydrogen bond definition, in light of recent evidence about its true nature. The International Union of Pure and Applied Chemistry's (Iupac's) Physical and Biophysical Chemistry Division has now published its proposal for the revised definition, and the chemical community has until the end of March 2011 to respond. Barring significant objections, it will be adopted shortly thereafter.
Two key factors are motivating the bonding interaction's redefinition. One is a shift in the traditional view that a hydrogen bond is a purely electrostatic attraction between dipoles or charges on a hydrogen and another, electronegative, atom. Elangannan Arunan, who co-chairs the Iupac group assigned to categorise hydrogen bonds and other intermolecular interactions, highlights that there is a variety of evidence, including nuclear magnetic resonance data, that some electron density is shared between them. 'This shows that the hydrogen bond has a covalent nature,' he says.
The current classification also concentrates on fluorine, oxygen and nitrogen, which Arunan says research has been shown as too simplistic. 'Most existing definitions insist hydrogen is connected to the most electronegative atoms,' he tells Chemistry World. 'That is far from complete now.' Arunan points out that Richard Nelmes at the University of Edinburgh, UK discovered that solid hydrogen sulfide has a hydrogen bonding structure resembling ice. 'That's what really shocked chemists,' he says. ...
by Andy Extance
Previously, the definition suggested hydrogen bonds were ‘electrostatic interactions’, where hydrogen atoms bear a slight positive charge that is attracted by a slightly negatively-charged bonding partner. The new definition allows there to be some element of covalent bonding involved, where electrons are formally shared between the atoms.[1]
[1]. http://blogs.nature.com/news/thegreatbeyond/2010/11/chemists_redefine_hydrogen_bon.html
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