Computational studies on the dimers and the thermal dimerization of norbornadiene

In this study, 14 norbornadiene (NBD) dimers and the thermal dimerization mechanism were studied using the hybrid density functional theory (B3LYP) and the second‐order multiconfigurational perturbation theory (CASPT2). In the process of dimerization, the biradical stationary points were located using the unrestricted, broken‐spin, symmetry approach. The pathways were divided into eight parts to aid the analysis of their mechanisms. Our results indicated that the process for the formation of the cage‐like heptacyclo[6.6.0.0. 2 , 6 0. 3 , 13 0. 4 , 11 0 5 , 9 .0 10 , 14 ] tetradecane (HCTD, D14) is highly exothermic (92.15 kcal/mol), indicating that D14 is the most stable NBD dimer. However, the formation of D14 is very difficult to achieve kinetically because of a higher barrier in the thermal dimerization. On the contrary, the formation of exo‐cis‐exo (D5) is kinetically favorable, but thermodynamically unfavorable at higher temperature. Therefore, the combination of both thermodynamic and kinetic factors indicated that the formation of exo‐exo (D9), which resembles the product of the pseudo‐Diels‐Alder addition, is most likely in the NBD dimerization. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008

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