Journal article

Authors list: Schreiner, PR; Karney, WL; Schleyer, PV; Borden, WT; Hamilton, TP; Schaefer, HF

Publication year: 1996

Pages: 7030-7039

Journal: The Journal of Organic Chemistry

Volume number: 61

Issue number: 20

ISSN: 0022-3263

DOI Link: https://doi.org/10.1021/jo960884y

Publisher: American Chemical Society

Abstract: 

The rearrangement of phenylcarbene (1) to 1,2,4,6-cycloheptatetraene (3)
has been studied theoretically, using SCF, CASSCF, CASPT2N, DFT
(B3LYP), CISD, CCSD, and CCSD(T) methods in conjunction with the 6-31G*,
6-311+G*, 6-311G(2d,p), cc-pVDZ, and DZd basis sets. Stationary points
were characterized by vibrational frequency analyses at
CASSCF(8,8)/6-31G* and B3LYP/6-31G*. Phenylcarbene (1) has a triplet ground state (³A‘‘) with a singlet−triplet separation (ΔE_ST) of 3−5 kcal mol^-1. In agreement with experiment, chiral 3 is the lowest lying structure on this part of the C₇H₆ potential energy surface. Bicyclo[4.1.0]hepta-2,4,6-triene (2) is an intermediate in the rearrangement of 1 into 3, but it is unlikely to be observable experimentally due to a barrier height of only 1−2 kcal mol^-1. The enantiomers of 3 interconvert via the ¹A₂ state of cycloheptatrienylidene (4) with an activation energy of 20 kcal mol^-1. The “aromatic” ¹A₁ state, previously believed to be the lowest singlet state of 4, is roughly 10 kcal mol^-1 higher in energy than the ¹A₂ state, and, in violation of Hund's rule, ³A₂ is also calculated to lie above ¹A₂ in energy. Thus, even if ³A₂ were populated, it is likely to undergo rapid intersystem crossing to ¹A₂. We suggest ³B₁-4 is the metastable triplet observed by EPR.

Harvard Citation style: Schreiner, P., Karney, W., Schleyer, P., Borden, W., Hamilton, T. and Schaefer, H. (1996) Carbene Rearrangements Unsurpassed:  Details of the C7H6 Potential Energy Surface Revealed, The Journal of Organic Chemistry, 61(20), pp. 7030-7039. https://doi.org/10.1021/jo960884y

APA Citation style: Schreiner, P., Karney, W., Schleyer, P., Borden, W., Hamilton, T., & Schaefer, H. (1996). Carbene Rearrangements Unsurpassed:  Details of the C7H6 Potential Energy Surface Revealed. The Journal of Organic Chemistry. 61(20), 7030-7039. https://doi.org/10.1021/jo960884y