Evidence of intramolecular hydrogen bonding from spectroscopic data

The band widths of absorption and fluorescence speck, of many compounds have been measured. Empirically it has been observed that the values of band width are unusually large for compounds in which intermolecular hydrogen bonding takes place. In addition, the existence of intramolecular hydrogen bonding is indicated in 2.5-diphenyl-1,3,4-oxadiazole (PPD) and 2-phenyl-5-(4-biphenylyl)-1,3.4-oxadiazole (PBD): - The bonding; is assumed to take place between the nitrogen atoms on the central ring and hydrogen atoms on adjacent phenyl rings. Although bonding to a hydrogen atom on a phenyl ring is not readily achieved, a planar configuration is expected to facilitate this type of interaction in the above compounds.