Cyclooctatetraene Computational Photo- and Thermal Chemistry: A Reactivity Model for Conjugated Hydrocarbons
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- 作者：Marco Garavelli ; Fernando Bernardi ; Alessandro Cembran ; Obis Castañ ; o ; Luis Manuel Frutos ; Manuela Merchá ; n ; and Massimo Olivucci
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：November 20, 2002
- 年：2002
- 卷：124
- 期：46
- 页码：13770 - 13789
- 全文大小：877K
- 年卷期：v.124,no.46(November 20, 2002)
- ISSN：1520-5126
文摘
We use ab initio CASSCF and CASPT2 computations to construct the composite multistaterelaxation path relevant to cycloocta-1,3,5,7-tetraene singlet photochemistry. The results show that anefficient population of the dark excited state (S1) takes place after ultrafast decay from the spectroscopicexcited state (S2). A planar D8h-symmetric minimum represents the collecting point on S1. Nonadiabatictransitions to S0 appear to be controlled by two different tetraradical-type conical intersections, which aredirectly accessible from the S1 minimum following specific excited-state reaction paths. The higher-energyconical intersection belongs to the same type of intersections previously documented in linear and cyclicconjugated hydrocarbons and features a triangular -(CH)3- kink. This point mediates both cis 
transphotoisomerization and cyclopropanation reactions. The lowest energy conical intersection has a boat-shaped structure. This intersection accounts for production of semibullvalene or for double-bond shifting.The mapping of both photochemical and thermal reaction paths (including also Cope rearrangements,valence isomerizations, ring inversions, and double-bond shifting) has allowed us to draw a comprehensivereactivity scheme for cyclooctatetraene, which rationalizes the experimental observations and documentsthe complex network of photochemical and thermal reaction path interconnections. The factors controllingthe selection and accessibility of a number of conjugated hydrocarbon prototype conical intersections andground-state relaxation channels are discussed.
transphotoisomerization and cyclopropanation reactions. The lowest energy conical intersection has a boat-shaped structure. This intersection accounts for production of semibullvalene or for double-bond shifting.The mapping of both photochemical and thermal reaction paths (including also Cope rearrangements,valence isomerizations, ring inversions, and double-bond shifting) has allowed us to draw a comprehensivereactivity scheme for cyclooctatetraene, which rationalizes the experimental observations and documentsthe complex network of photochemical and thermal reaction path interconnections. The factors controllingthe selection and accessibility of a number of conjugated hydrocarbon prototype conical intersections andground-state relaxation channels are discussed.