Spin trapping with 5, 5-dimethylpyrroline-N-oxide (DMPO) of various radicals was carried out in aqueous solutions and the ESR parameters for the spin adduct radicals were determined. Comparison of hyperfine coupling constants obtained in aqueous solutions and in benzene revealed that considerable solvent effect exists. For the radical obtained by the addition of a hydroxyl radical to DMPO, the hyperfine coupling constant was found to depend on the basicity of the solution. This phenomenon was analyzed in terms of the acid dissociation equilibrium of the hydroxyl proton of the adduct radical, and the pK value was determined to be 12.96.
采用5,
5-二甲基-1-
吡咯啉氮氧化物(
DMPO)进行自旋捕获,在
水中制备了多种自由基,并测定了自旋加合物自由基的电子自旋共振(ESR)参数。比较在
水中和苯中获得的超精细耦合常数,揭示了显著的溶剂效应。对于通过羟基自由基加合到
DMPO上得到的自由基,其超精细耦合常数被发现依赖于溶液的碱度。这一现象基于加合物自由基中羟基质子的酸解离平衡进行了分析,并确定其pK值为12.96。