Dihydrogen bond: Difference between revisions

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| year = 1968
| doi = 10.1039/C19680001551
}}</ref> They observed intense absorptions in the [[IR spectroscopy|IR band]]s at 3300 and 3210&nbsp;cm<sup>−1</sup> for a solution of (CH<sub>3</sub>)<sub>2</sub>NHBH<sub>3</sub>. The higher energy band is assigned to a normal N-&minus;H vibration whereas the lower energy band is assigned to the same bond, which is interacting with the B&minus;H.<!--Use &minus;, not &ndash;, for a schematic single bond--> Upon dilution of the solution, the 3300&nbsp;cm<sup>−1</sup> band increased in intensity and the 3210&nbsp;cm<sup>−1</sup> band decreased, indicative of intermolecular association.
Interest in dihydrogen bonding was reignited upon the crystallographic characterization of the molecule [[ammonia borane|H<sub>3</sub>NBH<sub>3</sub>]]. In this molecule, like the one studied by Brown and Hazeltine, the hydrogen atoms on nitrogen have a partial positive charge, denoted H<sup>δ+</sup>, and the hydrogen atoms on boron have a partial negative charge, often denoted H<sup>δ-δ−</sup>.<ref>{{Cite journal
| doi = 10.1021/ar950150s
| volume = 29