Steric Modulations in the Reversible Dimerizations of Phenalenyl Radicals via Unusually Weak Carbon-Centered π- and σ-Bonds
作者:V. Zaitsev、S. V. Rosokha、M. Head-Gordon、J. K. Kochi
DOI:10.1021/jo051612a
日期:2006.1.1
self-associations of various tricyclic phenalenyl radicals lead reversibly to either π- or σ-dimers, depending on alkyl-substitution patterns at the α- and β-positions. Thus, the sterically encumbered all-β-substituted tri-tert-butylphenalenyl radical (2•) affords only the long-bonded π-dimer in dichloromethane solutions, under conditions in which the parent phenalenyl radical (1•) leads to only the σ-dimer. Further
取决于在α和β位置的烷基取代方式,各种三环菲基自由基的自发自缔合可逆地导致π或σ二聚体。因此,在空间上受全β-取代的三叔丁基苯菲基自由基(2 •)在母体菲烯基(1 •)仅导致σ-二聚体。进一步的产权负担1 •带有一对α,β-或β,β-叔丁基取代基,以及另外的甲基和乙基(如在空间位阻的菲烯基中3 •− 6 •)不会抑制σ-二聚体。ESR光谱已成功用于监测两个反磁性(2-电子)二聚体的形成;紫外可见光谱法通过其强烈的近红外波段专门鉴定了π-二聚体。这些菲基自由基的不同温度相关光谱(ESR和UV-vis)行为允许对σ-二聚体的12±2 kcal mol - 1的键焓进行定量评估,其中在理论上考虑到了异常低的值在形成这种键时,伴随着苯菲烯基(芳族)π-共振能量的大量损失。