Skip to main content
Article
Benzylic Cations with Triplet Ground States:  Computational Studies of Aryl Carbenium Ions, Silylenium Ions, Nitrenium Ions, and Oxenium Ions Substituted with Meta π Donors
Journal of the American Chemical Society (2007)
  • Arthur Winter, University of Maryland - College Park
  • Daniel E. Falvey, University of Maryland - College Park
  • Christopher J. Cramer, University of Minnesota - Twin Cities
  • Benjamin F. Gherman
Abstract

Density functional theory (B3LYP/6-31G(d,p)) was used to predict the effect of meta substitution on aryl cationic (Ar−X+) species, including aryloxenium ions, arylsilylenium ions, arylnitrenium ions, and arylcarbenium ions. Multireference second-order perturbation theory (CASPT2) calculations were used to benchmark the quantitative accuracy of the DFT calculations for representative systems. Substituting the meta positions on these species with π donors stabilizes a π,π* diradical state analogous to the well-known m-xylylene diradical. Notably, the 3,5-bis(N,N-dimethylamino)benzyl cation is predicted to have a triplet ground state by 1.9 kcal/mol by DFT and to have essentially degenerate singlet−triplet states at the CASPT2(10,9) level of theory. Adding electron-withdrawing CF3 groups to the exocyclic carbon of this meta-disubstituted benzyl cation further increases the predicted singlet−triplet gap in favor of the triplet. Other aryl cationic species substituted with strong π electron-donating groups in the meta positions are predicted to have low-energy or ground-state triplet states. Systems analogous to the naphthaquinodimethane diradicals are also reported.

Publication Date
2007
Publisher Statement
Reprinted (adapted) with permission from J. Am. Chem. Soc., 2007, 129 (33), pp 10113–10119. Copyright 2007 American Chemical Society.
Citation Information
Arthur Winter, Daniel E. Falvey, Christopher J. Cramer and Benjamin F. Gherman. "Benzylic Cations with Triplet Ground States:  Computational Studies of Aryl Carbenium Ions, Silylenium Ions, Nitrenium Ions, and Oxenium Ions Substituted with Meta π Donors" Journal of the American Chemical Society Vol. 129 Iss. 33 (2007)
Available at: http://works.bepress.com/arthur_winter/20/