SOLVENT EFFECTS OF 1,4-BENZOQUINONE AND ITS ANION-RADICALS PROBED BY RESONANCE RAMAN AND ABSORPTION-SPECTRA AND THEIR CORRELATION WITH REDOX POTENTIALS

Resonance Raman (RR) and absorption spectra and cyclic voltammograms w ere measured for 1,4-benzoquinone (BQ) and its anion radical (BQ(-)') in various solvents. The absorption maxima of BQ(-)' around 440 and 32 0 nm exhibit a good linear correlation both with acceptor numbers (AN) of solvents and the standard reduction potentials of BQ. The wavenumb ers of v(8a) (Wilson's notation, C=C stretch) and v(9a) (C-H in-plane deformation) of BQ show linear correlations with the polarizabilities and dielectric constants of solvents, respectively. The v(8a) and v(7a ) (C=O stretch) wavenumbers of BQ(-)' can be linearly correlated with solvent AN. In addition, the standard reduction potentials of BQ also show good linear correlations with both solvent AN and wavenumbers of v(8a) of BQ(-'). These results cannot be interpreted by simple hydroge n bonding interactions of carbonyl oxygen with solvent but rather sugg est that the pi-electrons of BQ(-)' and BQ serve as an If-bond accepto r, forming novel II-bonds with the solvent. The magnitude of the novel II-bond interaction is estimated to be ca 7 and ca. 35 heal mol(-1) o r less for BQ(-)' and BQ in water, respectively. (C) 1998 John Wiley & Sons, Ltd.