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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >General Method for Determining Redox Potentials without Electrolyte
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General Method for Determining Redox Potentials without Electrolyte

机译：用于确定无电解质的氧化还原电位的一般方法

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摘要

A novel method to determine redox potentials without electrolyte is presented. The method is based on a new ability to determine the dissociation constant, K degrees(d), for ion pairs formed between any radical anion and any inert electrolyte counterion. These dissociation constants can be used to determine relative shifts of redox potential as a function of electrolyte concentration, connecting referenced potentials determined with electrochemistry (with 0.1 M electrolyte) to electrolyte-free values. Pulse radiolysis created radical anions enabling determination of equilibrium constants for electron transfer between anions of donor and acceptor molecules as a function of electrolyte concentration in THF. The measurements determined "composite equilibrium constants", K-eqC, which contain information about the dissociation constant for the electrolyte cations, X+, with the radical anions of both the donor, K degrees(d)(D-center dot,X+) and the acceptor, K degrees(d)(A(-center dot),X+). Dissociation constants were obtained for a selection of radical anions with tetrabutylammonium (TBA(+)). The electrolyte was found to shift the reduction potentials of small molecules 1-methylpyrene and trans-stilbene by close to +130 mV whereas oligo-fluorenes and polyfluorenes experienced shifts of only (+25 +/- 6) mV due to charge delocalization weakening the ion pair. These shifts for reduction of aromatic hydrocarbon molecules are smaller than shifts of +232 and +451 mV seen previously for benzophenone radical anion with TBA(+) and Na+ respectively where the charge on the radical anion is localized largely on one C=O bond, thus forming a more tightly bound ion pair.
机译：提出了一种确定没有电解质的氧化还原电位的新方法。该方法基于确定在任何自由基阴离子和任何惰性电解质抗衡离子之间形成的离子对的解离常数K度（d）的新能力。这些解离常数可用于确定作为电解质浓度的函数的氧化还原电位的相对变化，将用电化学（用0.1M电解质）测定的参考电位连接到无电解质值。脉冲辐射产生自由基阴影，从而能够测定供体和受体分子的阴离子之间的电子转移的均衡常数作为THF的电解质浓度的函数。测量确定了“复合平衡常数”，K-EQC，其含有关于电解质阳离子的解离常数的信息，X +，具有供体，K度（D-Center Dot，X +）的自由基阴离子和受体，k度（d）（a（ - center dot），x +）。获得与四丁基铵（TBA（+））选择的基团阴离子的离解常数。发现电解质将小分子1-甲基芘和反式芪的还原电位靠近+130 mV，而寡聚醇和多氟烯烃由于电荷描向削弱而仅有（+25 +/- 6）MV的换档离子对。这些芳烃分子还原的变化小于先前对于用TBA（+）和Na +的二苯甲酮自由基观察到的+232和+ 451mV的偏移，其中在自由基阴离子上的电荷很大于一个C = O键，因此形成更紧密的离子对。

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