Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
J Am Chem Soc. 2011 Apr 6;133(13):5086-93. doi: 10.1021/ja1114612. Epub 2011 Mar 8.
The geometries and energies of the electronic states of phenyloxenium ion 1 (Ph-O(+)) were computed at the multireference CASPT2/pVTZ level of theory. Despite being isoelectronic to phenylnitrene 4, the phenyloxenium ion 1 has remarkably different energetic orderings of its electronic states. The closed-shell singlet configuration ((1)A(1)) is the ground state of the phenyloxenium ion 1, with a computed adiabatic energy gap of 22.1 kcal/mol to the lowest-energy triplet state ((3)A(2)). Open-shell singlet configurations ((1)A(2), (1)B(1), (1)B(2), 2(1)A(1)) are significantly higher in energy (>30 kcal/mol) than the closed-shell singlet configuration. These values suggest a revision to the current assignments of the ultraviolet photoelectron spectroscopy bands for the phenoxy radical to generate the phenyloxenium ion 1. For para-substituted phenyloxenium ions, the adiabatic singlet-triplet energy gap (ΔE(ST)) is found to have a positive linear free energy relationship with the Hammett-like σ(+)(R)/σ(+) substituent parameters; for meta substituents, the relationship is nonlinear and negatively correlated. CASPT2 analyses of the excited states of p-aminophenyloxenium ion 5 and p-cyanophenyloxenium ion 10 indicate that the relative orderings of the electronic states remain largely unperturbed for these para substitutions. In contrast, meta-donor-substituted phenyloxenium ions have low-energy open-shell states (open-shell singlet, triplet) due to stabilization of a π,π* diradical state by the donor substituent. However, all of the other phenyloxenium ions and larger aryloxenium ions (naphthyl, anthryl) included in this study have closed-shell singlet ground states. Consequently, ground-state reactions of phenyloxenium ions are anticipated to be more closely related to closed-shell singlet arylnitrenium ions (Ar-NH(+)) than their isoelectronic arylnitrene (Ar-N) counterparts.
苯氧鎓离子 1（Ph-O(+)）的电子态的几何形状和能量在多参考 CASPT2/pVTZ 理论水平上进行了计算。尽管与苯亚硝胺 4 等电子，但苯氧鎓离子 1 的电子态的能级序明显不同。闭壳层单重态构型（(1)A(1)）是苯氧鎓离子 1 的基态，计算得到的绝热能隙为 22.1 kcal/mol，至最低能量三重态（(3)A(2)）。开壳层单重态构型((1)A(2)、(1)B(1)、(1)B(2)、2(1)A(1))的能量明显高于闭壳层单重态构型（>30 kcal/mol）。这些值表明需要修正当前的苯氧基自由基的紫外光电子能谱带的分配，以生成苯氧鎓离子 1。对于对位取代的苯氧鎓离子，发现绝热单重态-三重态能量隙（ΔE(ST)）与哈米特型σ(+)(R)/σ(+)取代基参数呈正线性自由能关系；对于间位取代，关系是非线性的且呈负相关。对位取代的 p-氨基苯氧鎓离子 5 和 p-氰基苯氧鎓离子 10 的激发态的 CASPT2 分析表明，这些取代基对电子态的相对顺序影响不大。相比之下，由于供电子取代基稳定了π,π*双自由基态，间位供电子取代的苯氧鎓离子具有低能开壳层态（开壳层单重态、三重态）。然而，本研究中包含的所有其他苯氧鎓离子和较大的芳氧鎓离子（萘基、蒽基）都具有闭壳层单重态基态。因此，预计苯氧鎓离子的基态反应将与闭壳层单重态芳基亚硝胺离子（Ar-NH(+)）更密切相关，而不是与其等电子的芳基亚氮（Ar-N）对应物。
