Spectral Properties and Reactivity of Diarylmethanol Radical Cations in Aqueous Solution. Evidence for Intramolecular Charge Resonance<sup>1</sup>
作者:Massimo Bietti、Osvaldo Lanzalunga
DOI:10.1021/jo016287f
日期:2002.4.1
Spectral properties and reactivities of ring-methoxylated diarylmethane and diarylmethanol radical cations, generated in aqueous solution by pulse and gamma-radiolysis and by the one-electron chemical oxidant potassium 12-tungstocobalt(III)ate, have been studied. The radical cations display three bands in the UV, visible, and vis-NIR regions of the spectrum. The vis-NIR band is assigned to an intramolecular
研究了在水溶液中通过脉冲和伽马射线分解以及单电子化学氧化剂12-钨钴(III)生成的环甲氧基化二芳基甲烷和二芳基甲醇自由基阳离子的光谱性质和反应活性。自由基阳离子在光谱的UV,可见光和vis-NIR区域显示三个波段。vis-NIR谱带被分配给中性供体和带电受体环之间的分子内电荷共振相互作用(CR),这可以通过观察发现,vis-NIR谱带相对于UV和可见谱带的相对强度底物浓度的增加不会增加,并且该带的位置和强度受环取代模式的影响。在酸性溶液(pH = 4)中,单甲氧基化的二芳基甲醇自由基阳离子1a。(+-)1e。(+)通过酮基自由基介导的Cα-H去质子化[k =(1.7-1.9)x 10(4)s(-1)]衰减,该酮基进一步被氧化时间分辨光谱法和产物研究均证明,反应介质可生成相应的二苯甲酮。使用二甲氧基化自由基阳离子2。(+),Cα-H的去质子化反而要慢得多(k = 6.7 x 10(2)s(