![](https://d3ilqtpdwi981i.cloudfront.net/-UosdyMSIa2SKjioPm6U1E7TVsg=/425x550/smart/https://bepress-attached-resources.s3.amazonaws.com/uploads/9c/b9/ee/9cb9eee1-bd71-4604-81f5-b28af6b49387/thumbnail_fe6bc31b-5a4a-4616-9e90-622dd11370af.jpg)
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.
Available at: http://works.bepress.com/arthur_winter/2/
Reprinted (adapted) with permission from J. Phys. Chem. A, 2012, 116 (37), pp 9398–9403. Copyright 2012 American Chemical Society.