An MC-SCF/MP2 Study of the Photochemistry of 2,3-Diazabicyclo[2.2.1]hept-2-ene: Production and Fate of Diazenyl and Hydrazonyl Biradicals
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- 作者：Naoko Yamamoto ; Massimo Olivucci ; Paolo Celani ; Fernando Bernardi ; and Michael A. Robb
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：March 18, 1998
- 年：1998
- 卷：120
- 期：10
- 页码：2391 - 2407
- 全文大小：282K
- 年卷期：v.120,no.10(March 18, 1998)
- ISSN：1520-5126
文摘
A CAS-SCF/MP2 study of the photolysis of2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) has beencarriedout with use of a 6-31G* basis. The S1 (n-
*),T1 (n-*), and T2 (-*) reactionpaths for deazetization(via 
C-N cleavage) and rearrangement reaction to azirane (via 
C-C cleavage) have been investigatedalong with the associated reaction pathways for cyclization andrearrangement of the photoproduct,1,3-cyclopentanediyl biradical. It is shown that singlet andtriplet photoexcited DBH evolve along a networkof 18 ground and excited-state intermediates, 17 transition structuresand 10 "funnels", where internal conversion(IC) or intersystem crossing (ISC) occurs. Three cyclicexcited-state species are reached following evolutionfrom the Franck-Condon region: two metastable singlet (n-*)and triplet (n-*) species and a stableexcited state3(n-*)-3(-*)intermediate. It is demonstrated that the singlet1(n-*) intermediate candecay directly to S0 or undergo ISC to generate the3(n-*)-3(-*)intermediate or/and the 3(n-*)intermediate. The 3(n-*) intermediate candirectly decay to the T1 diazenyl biradical or undergo ICtogenerate the3(n-*)-3(-*)intermediate. Finally, the much more stable3(n-*)-3(-*)intermediatecannot be converted to the other excited state intermediates but canonly react via either C-N and C-Ccleavage. Our computed energetics suggest that the3(n-*)-3(-*)intermediate is the best candidate forthe experimentally observed transient tripletintermediate.
*),T1 (n-*), and T2 (-*) reactionpaths for deazetization(via C-N cleavage) and rearrangement reaction to azirane (via C-C cleavage) have been investigatedalong with the associated reaction pathways for cyclization andrearrangement of the photoproduct,1,3-cyclopentanediyl biradical. It is shown that singlet andtriplet photoexcited DBH evolve along a networkof 18 ground and excited-state intermediates, 17 transition structuresand 10 "funnels", where internal conversion(IC) or intersystem crossing (ISC) occurs. Three cyclicexcited-state species are reached following evolutionfrom the Franck-Condon region: two metastable singlet (n-*)and triplet (n-*) species and a stableexcited state3(n-*)-3(-*)intermediate. It is demonstrated that the singlet1(n-*) intermediate candecay directly to S0 or undergo ISC to generate the3(n-*)-3(-*)intermediate or/and the 3(n-*)intermediate. The 3(n-*) intermediate candirectly decay to the T1 diazenyl biradical or undergo ICtogenerate the3(n-*)-3(-*)intermediate. Finally, the much more stable3(n-*)-3(-*)intermediatecannot be converted to the other excited state intermediates but canonly react via either C-N and C-Ccleavage. Our computed energetics suggest that the3(n-*)-3(-*)intermediate is the best candidate forthe experimentally observed transient tripletintermediate.