2101d Hach Hall, Department of Chemistry, Iowa State University, Ames, Iowa, USA.
J Phys Chem A. 2012 Sep 20;116(37):9398-403. doi: 10.1021/jp306817j. Epub 2012 Sep 10.
The electronic state orderings and energies of heteroaryl oxenium ions were computed using high-level CASPT2//CASSCF computations. We find that these ions have a number of diverse, low-energy configurations. Depending on the nature of the heteroaryl substituent, the lowest-energy configuration may be open-shell singlet, closed-shell singlet, or triplet, with further diversity found among the subtypes of these configurations. The 2- and 3-pyridinyl oxenium ions show small perturbations from the phenyl oxenium ion in electronic state orderings and energies, having closed-shell singlet ground states with significant gaps to an n,π* triplet state. In contrast, the 4-pyridinyl oxenium ion is computed to have a low-energy nitrenium ion-like triplet state. The pyrimidinyl oxenium ion is computed to have a near degeneracy between an open-shell singlet and triplet state, and the pyrizidinyl oxenium ion is computed to have a near-triple degeneracy between a closed-shell singlet state, an open-shell singlet state, and a triplet state. Therefore, the ground state of these latter heteroaryl oxenium ions cannot be predicted with certainty; in principle, reactivity from any of these states may be possible. These systems are of fundamental interest for probing the spin- and configuration-dependent reactivity of unusual electronic states for this important class of reactive intermediate.
使用高精度 CASPT2//CASSCF 计算方法，计算了杂芳氧鎓离子的电子态序和能量。我们发现这些离子具有多种低能量的构型。根据杂芳基取代基的性质，最低能量的构型可能是单重态开壳、单重态闭壳或三重态，这些构型的亚型中还存在进一步的多样性。2-和 3-吡啶基氧鎓离子在电子态序和能量方面与苯氧鎓离子仅有微小的扰动，具有单重态闭壳基态，与 n,π*三重态之间存在显著的能隙。相比之下，4-吡啶基氧鎓离子被计算为具有低能量的氮烯离子样三重态。嘧啶基氧鎓离子被计算为具有单重态和三重态之间的近简并性，吡嗪基氧鎓离子被计算为具有单重态闭壳、单重态开壳和三重态之间的近三重简并性。因此，这些杂芳基氧鎓离子的基态不能被确定地预测；原则上，来自这些态中的任何一个的反应性都可能是可能的。这些系统对于探测这种重要的反应中间体中不寻常电子态的自旋和构型依赖性反应性具有基本的兴趣。
