TY - JOUR
T1 - Benzylic cations with triplet ground states
T2 - Computational studies of aryl carbenium ions, silylenium ions, nitrenium ions, and oxenium ions substituted with meta π donors
AU - Winter, Arthur H.
AU - Falvey, Daniel E.
AU - Cramer, Christopher J.
AU - Gherman, Benjamin F.
PY - 2007/8/22
Y1 - 2007/8/22
N2 - 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 wellknown 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 stales. Systems analogous to the naphthaquinodimethane diradicals are also reported.
AB - 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 wellknown 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 stales. Systems analogous to the naphthaquinodimethane diradicals are also reported.
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U2 - 10.1021/ja070143m
DO - 10.1021/ja070143m
M3 - Article
C2 - 17655230
AN - SCOPUS:34548189449
SN - 0002-7863
VL - 129
SP - 10113
EP - 10119
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 33
ER -