Tetrahydrobenzenes: Singlet-triplet separations and vibrational frequencies
The energies and structures of the three tetradehydrobenzene (C{sub 6}H{sub 2}) isomers (ortho, meta, and para) were studied employing density functional theory (BLYP and B3LYP), complete active space SCF (CASSCF), and the coupled-cluster method with single, double (CCSD), and perturbative triple excitations [CCSD(T)] in conjunction with basis sets of up to triple-{zeta} plus double polarization quality. The meta isomer, 1,2,3,5-tetradehydrobenzene, is the most favorable cyclic isomer, but is 38 kcal mol{sup {minus}1} less stable than the hexatriyne C{sub 6}H{sub 2} global minimum. All of the cyclic isomers have singlet ground states, but these are less stable for the ortho and para isomers; hence, the singlet-triplet energy splittings for 1,2,4,5- and 1,2,3,4-tetradehydrobenzene are smaller than for ortho-benzyne. Harmonic vibrational frequency analyses [up to CCSD(T)/TZ2P] suggest that the {nu}{sub as}(C{triple{underscore}bond}C) vibration should be observable in the IR spectra of 1,2,4,5-tetradehydrobenzene at ca. 1,675 cm{sup {minus}1} but that this vibration might be too weak to be seen for 1,4-bis(trifluoromethyl)-2,3,5,6-tetradehydrobenzene.
- Research Organization:
- Univ. of Georgia, Athens, GA (US)
- Sponsoring Organization:
- Deutsche Forschungsgemeinschaft; Fonds der Chemischen Industrie; US Department of Energy
- DOE Contract Number:
- FG02-97ER14748
- OSTI ID:
- 20013114
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 12 Vol. 121; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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