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The Contributions of Through-Bond Interactions to the Singlet−Triplet Energy Difference in 1,3-Dehydrobenzene

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journal contribution
posted on 24.09.2009, 00:00 by Haiyan Wei, David A. Hrovat, Yirong Mo, Roald Hoffmann, Weston Thatcher Borden
Separation of the through-space (TS) from the through-bond (TB) interactions between the two atomic orbitals at C(1) and C(3) of 1,3-dehydrobenzene (1) has been achieved by carrying out ab initio, valence-bond, self-consistent-field (VBSCF) calculations. The results indicate that, at the CCSD(T)/cc-pVTZ optimized geometry of the singlet state of 1, the stabilization provided by TB interactions contributes 10% more than the stabilization provided by the TS interactions to the adiabatic singlet−triplet energy difference. The highest occupied MO of 1 contains a contribution from a hybrid AO at C(2), which has the same phase as the smaller lobes of the AOs at C(1) and C(3). Consequently, TB interactions in 1 increase with decreasing values of the C(1)C(3) distance. The origin of this hybrid AO at C(2) and the contributions of hyperconjugation to TB and TS interactions in 1 are described and discussed.