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Excited states and photochemical reactivity of fulvene. A theoretical study (1994)

Dreyer, Jens ; Klessinger, Martin

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 101 (1994), S. 10655-10665

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Semiempirical and ab initio calculations including electron correlation have been carried out for the ground and excited states of fulvene. Vertical singlet and triplet excitation energies including several Rydberg transitions, which have been calculated using an extended basis set augmented with even tempered diffuse functions, are in good agreement with experiment. Spectroscopic minima were obtained for the 1A1(S2) and 3B2(T1) states of planar fulvene, and on the semiempirical level also for the 1A‘(S1) state, which is only of Cs symmetry. Twisting of the exocyclic double bond was studied by means of correlation diagrams as well as by calculating potential energy hypersurfaces. At 90° twist all stationary points are identified as transition states at the ab initio level, while two minima (S0 and S2) and one transition state (T1) result from the semiempirical calculations. Taking into account pyramidalization of the exocyclic methylene group yields a minimum for the T1 state and a conical intersection of the S1 and S0 states, which is not identical with the one that is to be expected for a critically heterosymmetric biradicaloid. The photochemistry of fulvene is being discussed in the light of the present results. © 1994 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.467879

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The photochemical Formation of Fulvene from Benzene via Prefulvene-a Theoretical StudyDedicated to Professor Roy McWeeny on the occasion of his 70th birthday (1996)

Dreyer, Jens ; Klessinger, Martin

Weinheim : Wiley-Blackwell

Chemistry - A European Journal 2 (1996), S. 335-341

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ISSN: 0947-6539

Keywords: ab initio calculations ; benzene ; fulvene ; isomerization ; photochemistry ; Chemistry ; General Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Results of semiempirical MN-DOC-CI and ab initio CASSCF calculations reveal that fulvene is a primary product of the photolysis of benzene. The photochemical step is assumed to lead to prefulvene, and both a synchronous conversion and a two-step process via bicyclo[3.1.0]hexa-1,3-diene (isofulvene) could be ruled out as possible pathways from prefulvene to benzene. The most probable mechanism for the photochemical isomerization of benzene to fulvene involves the intermediate structures prefulvene and 1,3-cyclopentadienylcarbene and has to compete with the almost barrierless formation of benzvalene and rearomatization to benzene. The short-lived intermediates are rather flexible structures with negligible barriers to inversion at the radical center in the threemembered ring of prefulvene and prebenzvalene and to rotation around the exocyclic single bond in 1,3-cyclopentadienylcarbene.

Additional Material: 10 Ill.