The charge-transfer mechanism of hydrogen bonding as revealed from electronic absorption spectra^(*)

Institute for Solid State Physics, the University of Tokyo, Japan.

Abstract

It was found that the hydrogen maleate anion exhibits a strong absorption band at 211 mμ whereas maleic acid and its dinegative ion show absorption bands in the wavelenght region shorter than 200 mμ. The direction of transition moment of the 211 mμ band was determined to be almost parallel with the O — H...O^– line. Combining these experimental results with theoritical considerations made for the σ-electron system of O — H...O^– and also for the π-electron systems of the hydrogen maleate anion and the dinegative ion, we concluded that the 211 mμ band may be regarded as the charge-transfer band pertinent to the O — H...O^– hydrogen bonding system ; namely, as the band due to the transition between the ground and excited energy levels caused by the following resonance interaction :

O — H...O^– ↔ O^–...H — O