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Quantum Chemical Characterization of Low-energy States of Calicene in the Gas Phase and Solution

Ghigo, Giovanni
Solstad, Lee M.
Cramer, Christopher J.
Published in Journal of Organic Chemistry. 2007, vol. 72, no. 8, p. 2823-2831
Abstract The ground and excited electronic state properties of calicene (triapentafulvalene or 5-(cycloprop-2-en-1-ylidene)cyclopenta-1,3-diene) have been studied with a variety of density functional models (mPWPW91, PBE, TPSS, TPSh, B3LYP) and post-Hartree−Fock models based on single (MP2 and CCSD(T)) and multideterminantal (CASPT2) reference wave functions. All methods agree well on the properties of ground-state calicene, which is described as a conjugated double bond system with substantial zwitterionic character deriving from a charge-separated mesomer in which the three- and five-membered rings are both aromatic. Although the two rings are joined by a formal double bond, contributions from the aromatic mesomer reduce its bond order substantially. A rotational barrier of 40−41 kcal mol-1 is predicted in the gas phase and solvation effects reduce the barrier to 37 and 33 kcal mol-1 in benzene and water, respectively, because of increased zwitterionic character in the twisted transition-state structure. Multi-state CASPT2 (MS-CASPT2) is used to characterize the first few excited singlet and triplet states and indicates that the most important transition occurs at 4.93 eV (251 nm). A cis−trans photoisomerization about the inter-ring double bond is found to be inefficient.
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Research group Groupe Gagliardi
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GHIGO, Giovanni et al. Quantum Chemical Characterization of Low-energy States of Calicene in the Gas Phase and Solution. In: Journal of Organic Chemistry, 2007, vol. 72, n° 8, p. 2823-2831. https://archive-ouverte.unige.ch/unige:3197

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Deposited on : 2009-09-21

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