取代苯醌在乙腈中的电化学和光谱电化学研究

研究了含有甲基、甲氧基、氟或氯等不同取代基的对苯醌衍生物在乙腈中的电化学和紫外-可见光谱电化学性质,并探讨了取代基对化合物电化学性质的影响.结果表明,每个化合物均可以发生两步可逆的单电子还原反应,分子中的供电子基能使还原反应电位发生负移,而吸电子基则可使电位发生正移.还原电位的变化值(ΔE)与取代基哈密特常数(∑σ)之间呈线性关系,其方程为:ΔE1=0.386 9∑σ-0.073 5(V),R2=0.996,ΔE2=0.280 3∑σ-0.114 5(V),R2=0.981.在控制电位还原时化合物的紫外可见光谱具有明显的变化,表明两步还原反应的产物分别为阴离子自由基(R)nQ.-和负二价阴离子(R)nQ2-(R=—CH3,—OCH3,—Cl,—F;n=0～4).

Electrochemistry and spectroelectrochemistry of substituted p-benzoquinones in acetonitrile

Electrochemical and UV-visible spectroelectrochemical properties of eight substituted p-benzoquinones were examined in acetonitrile containing 0.1 mol·L-1 tetra-n-butylammonium perchlorate as supporting electrolyte.The investigated compounds are represented as(R)nQ,where Q is a p-benzoquinone,R=—OCH3,—CH3,—F or —Cl and n= 1～4.Each compound undergoes two reversible one-electron reductions in CH3CN.A negative shift is observed in both the first and second reduction potentials for compounds containing electron-donating substituents(—CH3 or —OCH3),but a positive potential shift is seen for compound having electron-withdrawing groups(—F or —Cl) as compared to the unsubstituted benzoquinone(Q).Linear relationships were obtained between the potential shifted(Δ∑) and the sum of Hammett substituent constants(∑σ).The equations of the correlation are ΔE1=0.386 9∑σ-0.073 5 V(R2=0.996) and ΔE2=0.280 3∑σ-0.114 5 V(R2=0.981) for the first and second reductions,respectively.UV-visible spectral changes obtained under application of an applied potential indicate that a π-anion radical and dianion were generated during the first and second controlled potential reductions of the compounds under the given solution conditions.