Probing hydrogen bonding to quinone anion radicals by 1H and 2H ENDOR spectroscopy at 35 GHz

ENDOR spectroscopy at 35 GHz and 80 K was used to study the radical anion of 1,4-benzoquinone (BQ) in water and various alcohols. BQ(-.)-d(4) in H2O and BQ(-.)-h(4) in D2O were investigated with the aim to obtain information on the hydrogen bonds between the quinone oxygen and the respective solvent. The observed spectra were analyzed using the GENDOR program for the simulation of orientationally selected powder ENDOR spectra. From the spectral simulations the hyperfine coupling and nuclear quadrupolar coupling tensor components and the angles with respect to the quinone axes were obtained. Hydrogen bond lengths and geometries were deduced from the hyperfine couplings using the point-dipole model and from the nuclear quadrupolar couplings using empirical relationships. The experimental results were compared, and found to be in fair agreement, with those derived from Density Functional Theory (DFT) calculations performed on geometry optimized structures of solute and solvent. (C) 2003 Elsevier B.V. All rights reserved.