Campus Units

Chemistry

Document Type

Article

Publication Version

Published Version

Publication Date

2011

Journal or Book Title

Journal of the American Chemical Society

Volume

133

Issue

13

First Page

5086

Last Page

5093

DOI

10.1021/ja1114612

Abstract

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 (1A1) 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 (3A2). Open-shell singlet configurations (1A2, 1B1, 1B2, 21A1) 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 (ΔEST) is found to have a positive linear free energy relationship with the Hammett-like σ+R+ 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.

Comments

Reprinted (adapted) with permission from J. Am. Chem. Soc., 2011, 133 (13), pp 5086–5093. Copyright 2011 American Chemical Society.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

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