TY - JOUR
T1 - Phenyloxenium ions
T2 - More like phenylnitrenium ions than isoelectronic phenylnitrenes?
AU - Hanway, Patrick J.
AU - Winter, Arthur H.
PY - 2011/4/6
Y1 - 2011/4/6
N2 - 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, 1B 1, 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 α+R/α+ 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.
AB - 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, 1B 1, 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 α+R/α+ 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.
UR - http://www.scopus.com/inward/record.url?scp=79953875427&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=79953875427&partnerID=8YFLogxK
U2 - 10.1021/ja1114612
DO - 10.1021/ja1114612
M3 - Article
C2 - 21384890
AN - SCOPUS:79953875427
SN - 0002-7863
VL - 133
SP - 5086
EP - 5093
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 13
ER -