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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Structure and Proton Reactivity of the Semiquinone Anion and Dianion of Biphenol in Water
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Structure and Proton Reactivity of the Semiquinone Anion and Dianion of Biphenol in Water

机译：水中双酚的半醌阴离子和双阴离子的结构和质子反应性

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Whether the redox intermediate state of 4,4'-biphenol in water, C_(12)H_8O_2~(-·), has a planar or staggered molecular geometry twisted about the inter-ring bond has been examined using time-resolved resonance Raman spectroscopy and electronic structure computation. Hydrogen-bonding effects on the p,p'-biphenylsemiquinone radical anion (C_(12)H_8O_2~(-·) structure were incorporated in the calculations by associating two water molecules with each oxygen site. The predicted structure, with inter-ring CC bond length of 1.455 A and dihedral angle of 17.7°, provides a good description of the spectroscopic observations. Hydrogen bonding slightly elongates the CO bonds, but its effect on the inter-ring twist is negligible. Nonequivalence of the tow phenyl rings, which are noncoplanar, is indicated by the resonance Raman spectra of C_(12)H_8O_2~(-·) in liquid water as well as in ethanol matrix at low temperatures. The π-conjugation between the rings is small in the radical anion, but greater than in its reduced dianion (C_(12)H_8O_2~(2-)) state, which signifies the role of torsional distortion of the molecular geometry in redox reactions of biphenyl systems. The change in the calculated CO bond length from the parent dianion to the p,p'-biphenylsemiquinone radical anion (0.031 A) is significantly smaller than that for the analogous p-benzosemiquinone radical anion system (0.049 A) and correlates well with the change in acid-base equilibria. The predictive value and limitations of the theoretical structure calculations of molecular ions and radidcals containing the X-C_6H_4O~- (X≠O) moiety, which occurs in a wide variety of chemical and biochemical redox systems, are examined.
机译：使用时间分辨共振拉曼光谱法研究了水中4,4'-双酚的氧化还原中间态C_（12）H_8O_2〜（-·）是否具有围绕环间键扭曲的平面或交错的分子几何结构和电子结构计算。通过将两个水分子与每个氧位点相关联，将氢键对p，p'-联苯半醌基阴离子（C_（12）H_8O_2〜（-·）结构的氢键作用纳入计算中。键长为1.455 A，二面角为17.7°，很好地说明了光谱学观察结果;氢键稍微延长了CO键，但对环间扭曲的影响可忽略不计。 C_（12）H_8O_2〜（-·）在低温下在液态水和乙醇基质中的共振拉曼光谱表明，它们之间的π共轭在自由基阴离子中很小，但大于在还原的二价阴离子（C_（12）H_8O_2〜（2-））状态下，表明分子几何结构的扭转畸变在联苯系统的氧化还原反应中的作用。 p，p'-联苯半醌自由基阴离子（0.031 A）明显小于类似的对-苯并半醌自由基阴离子系统（0.049 A），并且与酸碱平衡的变化密切相关。研究了在多种化学和生物化学氧化还原系统中发生的含有X-C_6H_4O〜-（X≠O）部分的分子离子和辐射基的理论结构计算的预测价值和局限性。

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