To understand solvation in room temperature ionic liquids (RTILs), an FT-EPR spectrum of alpha-hydroxydiphenylmethyl (HDPM) radical was measured in several RTILs of tert-alkylammonium or alkylimidazolium salts with anions of PF6-, BF4- (CF3SO2)(2)N-, CF3SO3-, WO42-, Cl- and Br-. The hyperfine coupling constant of the hydroxyl proton depends on Gutmann's donor number of the anion S, while the constants of phenyl alpha-protons are essentially the same for these RTILs. This result suggests the electron donor character of anions is important in HDPM solvation in RTILs through the anion-OH group hydrogen-bond. (c) 2005 Elsevier B.V.. All rights reserved.