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

Ghigo, Giovanni; Moughal Shahi, Abdul Rehaman; Gagliardi, Laura; Solstad, Lee M.; Cramer, Christopher J.

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Title		Quantum Chemical Characterization of Low-energy States of Calicene in the Gas Phase and Solution
Authors		Ghigo, Giovanni Moughal Shahi, Abdul Rehaman Gagliardi, Laura 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.
Identifiers		DOI: 10.1021/jo062420y
Full text		Article (Published version) - Free access Other version: http://pubs.acs.org/cgi-bin/article.cgi/joceah/2007/72/i08/pdf/jo062420y.pdf
Structures		Faculté des sciences / Section de chimie et biochimie / Département de chimie physique
Research group		Groupe Gagliardi
Citation (ISO format)		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