Complementary Effect of Intra- and Intermolecular Hydrogen Bonds on Electron Transfer in β-Hydroxy-Anthraquinone Derivatives.

We have carried out an electrochemical and theoretical study on the relationship between electron transfer (ET) and hydrogen bonding in 11 different 9,10-anthraquinone (AQ) derivatives, including β-hydroxy AQs and their methoxylated analogs, in the presence of hydrogen donors in acetonitrile (ACN). The complementary effects of the intra- and intermolecular hydrogen bonds (HBs) on ET were studied by analyzing the complex formation constants derived from the intermolecular HB. Our results revealed that the inductive effect of the β substituent that indirectly controls the charge distribution on the AQ carbonyl oxygen, and steric hindrance at the β position, affect the complex formation constants. Furthermore, the analysis of ET in different isomeric dihydroxy AQs suggested that the position of the hydroxy groups affects the charge distribution and stabilizes structures through conjugation of the quinone moiety including the ipso ring, controlling the intra- and intermolecular HBs complementarily.