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Red-, blue-, or no-shift in hydrogen bonds: A unified explanation

Jorly, Joseph and Jemmis, Eluvathingal D (2007) Red-, blue-, or no-shift in hydrogen bonds: A unified explanation. In: Journal of the American Chemical Society, 129 (15). pp. 4620-4632.

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We provide a simple explanation for X-H bond contraction and the associated blue shift and decrease of intensity in IR spectrum of the so-called improper hydrogen bonds. This explanation organizes hydrogen bonds (HBs) with a seemingly random relationship between the X-H bond length (and IR frequency and its intensity) to its interaction energy. The factors which affect the X-H bond in all X-H [midline ellipsis] Y HBs can be divided into two parts: (a) The electron affinity of X causes a net gain of electron density at the X-H bond region in the presence of Y and encourages an X-H bond contraction. (b) The well understood attractive interaction between the positive H and electron rich Y forces an X-H bond elongation. For electron rich, highly polar X-H bonds (proper HB donors) the latter almost always dominates and results in X-H bond elongation, whereas for less polar, electron poor X-H bonds (pro-improper HB donors) the effect of the former is noticeable if Y is not a very strong HB acceptor. Although both the above factors increase with increasing HB acceptor ability of Y, the shortening effect dominates over a range of Ys for suitable pro-improper X-Hs resulting in a surprising trend of decreasing X-H bond length with increasing HB acceptor ability. The observed frequency and intensity variations follow naturally. The possibility of HBs which do not show any IR frequency change in the X-H stretching mode also directly follows from this explanation.

Item Type: Journal Article
Publication: Journal of the American Chemical Society
Publisher: American Chemical Society
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 31 Jul 2007
Last Modified: 19 Sep 2010 04:38
URI: http://eprints.iisc.ac.in/id/eprint/11629

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