Radical Cations of Aromatic Selenium Compounds: Role of Se路路路X Nonbonding Interactions

详细信息    查看全文

• 作者：Beena G. Singh ; Elizabeth Thomas ; Shilpa N. Sawant ; Kohei Takahashi ; Kenchi Dedachi ; Michio Iwaoka ; K. Indira Priyadarsini
• 刊名：Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：September 26, 2013
• 年：2013
• 卷：117
• 期：38
• 页码：9259-9265
• 全文大小：302K
• 年卷期：v.117,no.38(September 26, 2013)
• ISSN：1520-5215

文摘

Selenium centered radical cations in aliphatic selenium compounds are stabilized by formation of two-center-three electron (2c鈥?e) hemi bonds either with nearby heteroatoms forming monomer radicals or with selenium atoms of the parent molecules forming dimer radicals. Such radicals in aromatic selenium compounds would generally be stabilized as monomers by the delocalization of the spin density along the aromatic ring. To test the assumption if aromatic selenides having Se路路路X nonbonding interactions can show different types of radical cations, we have performed pulse radiolysis studies of three structurally related aromatic selenium compounds and the results have been substantiated with cyclic voltammetry and quantum chemical calculations. The three aromatic selenium compounds have functional groups like 鈭扖H₂N(CH₃)₂ (1), 鈭扖H₂OH (2), and 鈭扖H₃ (3) at ortho position to the 鈭扴eCH₃ moiety. The energy of Se路路路X nonbonding interactions (E_nb) for these compounds is in the order 1 (Se路路路N) > 2 (Se路路路O) > 3 (Se路路路H). Radical cations, 1^鈥?, 2^鈥? and 3^鈥? were produced by the one-electron oxidation of 1, 2 and 3 by radiolytically generated ^{鈥?/sup>OH and Br₂鈥⑩€?/sup> radicals. Results on transient spectra, lifetime, and secondary reactions of 1鈥?, 2鈥?, and 3鈥? indicated that 1鈥? shows a significantly different absorption spectrum, longer lifetime, and less oxidizing power compared to those of 2鈥? or 3鈥?. Quantum chemical calculations suggested that 1鈥? is stabilized by the formation of a 2c鈥?e bond between Se and N atoms, whereas 2鈥? and 3鈥? acquire stability through the delocalization of the spin density on the aromatic ring. These results provide evidence for the first time that stronger nonbonding interactions between Se路路路N in the ground state, facilitate the formation of stabilized radical cations, which can significantly influence the redox chemistry and the biological activity of aromatic selenium compounds.}