Hydrogen bond
Hydrogen bonds can vary in strength from weak (1–2 kJ mol) to strong (161.5 kJ mol in the ion ). Typical enthalpies in vapor include:
Dihydrogen bond
In chemistry, a dihydrogen bond is a kind of hydrogen bond, an interaction between a metal hydride bond and an OH or NH group or other proton donor. With a van der Waals radius of 1.2 Å, hydrogen atoms do not usually approach other hydrogen atoms closer than 2.4 Å. Close approaches near 1.8 Å, are, however, characteristic of dihydrogen bonding.
An early example of this phenomenon is credited to Brown and Heseltine. They observed intense absorptions in the IR bands at 3300 and 3210 cm for a solution of (CH)NHBH. The higher energy band is assigned to a normal N−H vibration whereas the lower energy band is assigned to the same bond, which is interacting with the B−H. Upon dilution of the solution, the 3300 cm band increased in intensity and the 3210 cm band decreased, indicative of intermolecular association.