摘要：

The change in the position of the n →π* absorption bands on changing from a hydrocarbon to a hydroxylic solvent has been investigated for a number of molecules. The large shift to shorter wave lengths (blue-shift) is shown to be mainly due to hydrogen-bonding of the n-electrons by the hydroxylic solvent, which causes a greater stabilization of the ground state compared with the excited state of the molecule. Pyridazine and benzophenone have been examined in detail in a series of different mixtures of hexane and ethanol. The families of spectra obtained indicate that essentially two species are involved, a hydrogen bonded and a non-hydrogen bonded form and it is the formation of the hydrogen bonded species that causes the main shift of the n →π* transition to the blue. From the ultraviolet data, an association constant of hydrogen bonding can be obtained and this agrees well with the association constant found by a study of the association of ethanol with the molecule in the infrared. The infrared work makes use of the shift in the O-H stretching frequency on formation of a hydrogen bond.

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