Reduction potentials and kinetics of electron transfer reactions of phenylthiyl radicals: Comparisons with phenoxyl radicals
Reduction potentials and kinetics of electron transfer reactions of phenylthiyl radicals: Comparisons with phenoxyl radicals
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苯硫基电子转移反应的还原电位和动力学： 与苯氧基自由基的比较
DOI：
10.1021/jp960165n
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发表时间：
1996-06-06
影响因子：
--
通讯作者：
Schuler, RH
中科院分区：
文献类型：
--
作者：
Armstrong, DA;Sun, Q;Schuler, RH
测定了一些对位取代苯硫基自由基相对于标准氢电极的还原电位（E度（p-XC（6）H（4）S（.）/ p-XC（6）H（4）S（-））的电子转移平衡，并与已知还原电位的自由基进行了比较。这些还原电位已被证明是自洽的，介于0.02 V的对苯醌自由基阴离子和0.79 V的苯氧自由基之间。随着帕拉取代基的供电子能力的升高，还原电位降低。然而，取代基效应对于苯硫基自由基比它们的氧类似物弱得多。这些观察结果表明，硫原子和芳环系统之间的电子相互作用远小于氧原子。用Marcus理论对电子转移速率的研究表明，p-XC（6）H（4）O（.）和p-XC（6）H（4）S（.）H、CH_3和CH_3 O取代基对自由基的影响相似，但H_2N和O-帕拉取代基的重组能显著增加，而对p-XC（6）H（4）S（.）自由基比p-XC（6）H（4）O（.）根的这些观察结果是在雅阁与结构信息的自由基的光谱和理论研究表明，在后者的系统中的取代基与芳香族π系统强烈相互作用。
The reduction potentials relative to the standard hydrogen electrode (SHE) for a number of para-substituted phenylthiyl radicals (E degrees(p-XC(6)H(4)S(.)/p-XC(6)H(4)S(-))) have been derived from pulse radiolytic studies of electron transfer equilibria which compare their values to those of radicals of known reduction potentials, A ladder combining the reduction potentials for both phenylthiyl and phenoxyl radicals has been established. These reduction potentials have been shown to be self-consistent and are intermediate between those of p-benzosemiquinone radical anion at 0.02 V and phenoxyl radical at 0.79 V. The reduction potential decreases as the electron donating power of the para substituent rises, The substituent effect is, however, much weaker for the phenylthiyl radicals than for their oxygen analogs. These observations demonstrate that the electronic interaction between the sulfur atoms and the aromatic ring system is much less than that which occurs with oxygen atoms. Examination of the rates of electron transfer in terms of the Marcus theory indicates that the reorganization energies of both p-XC(6)H(4)O(.) and p-XC(6)H(4)S(.) radicals are similarly affected by H, CH3, and CH3O substitution, However, the reorganization energies increase substantially for H2N and O- para substituents with the effect being much less for the p-XC(6)H(4)S(.) radicals than for the p-XC(6)H(4)O(.) radicals. These observations are in accord with structural information from spectroscopic and theoretical studies of the radicals which show that in the latter system the substituent groups interact strongly with the aromatic pi system.