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Ground- and Excited-State Reactions of Norbornene and Isomers: A CASSCF Study and Comparison with Femtosecond Experiments

Wilsey, Sarah and Houk, K. N. and Zewail, A. H. (1999) Ground- and Excited-State Reactions of Norbornene and Isomers: A CASSCF Study and Comparison with Femtosecond Experiments. Journal of the American Chemical Society, 121 (24). pp. 5772-5786. ISSN 0002-7863. doi:10.1021/ja983480r.

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The ground-state and ^1(ππ^*)-state potential energy surfaces of norbornene and isomeric C_7H_(10) species were mapped using CASSCF theory and the 6-31G^* basis set and compared with the results of femtosecond experiments on norbornene retro Diels−Alder reactions. Computations explored stepwise and concerted retro Diels−Alder pathways, [1,3]-sigmatropic shifts, and [1,2]-sigmatropic shifts originating from the ^1(ππ^*)-state or ground-state surfaces. Extremely efficient decay occurs from the excited state to the ground state via two different conical intersections (surface crossings). The first of these crossing points is accessed by one-bond cleavage of C1−C6 (or C4−C5). Several possible subsequent ground-state reaction paths have been identified:  (a) ring-closure to form norbornene; (b) ring-closure to form bicyclo[3.2.0]hept-2-ene ([1,3]-sigmatropic shift); (c) formation of a metastable 1,3-biradical which closes to form tricyclo[^(3,7)]heptane ([1,2]-sigmatropic shift); and (d) collapse of a gauche-in biradical to a vibrationally excited cyclopentadiene and ethylene, or norbornene. Excited-state one-bond cleavage of C4−C7 (or C1−C7) leads to the second conical intersection. Possible ground-state reaction pathways from this structure lead to the formation of bicyclo[4.1.0]hept-2-ene ([1,3]-sigmatropic shift product) or to a second 1,3-biradical leading to tricyclo[^(3,7)]heptane ([1,2]-sigmatropic shift product). The vibrationally excited cyclopentadiene is the 220 fs lifetime species of mass 66 amu, consistent with the retro Diels−Alder reaction observed in the femtosecond laser experiments. It is proposed that biradicaloids formed after decay through the conical intersections are the 94 amu species, with an average lifetime of about 160 fs.

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URLURL TypeDescription ItemSupporting Information
Houk, K. N.0000-0002-8387-5261
Additional Information:© 1999 American Chemical Society. Received October 1, 1998. We thank Dr. Brett R. Beno for many helpful discussions and extensive results on the ground-state surface. We are grateful to the National Science Foundation for financial support of this research. This work was partially supported by the National Computational Science Alliance and utilized the NCSA SGI/Cray Powerchallenge Array. We also thank the San Diego Supercomputing Center and the UCLA Office of Academic Computing for computational resources. S.W. thanks the Royal Society for a NATO Fellowship and the Fulbright Commission for a scholarship.
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National Computational Science AllianceUNSPECIFIED
Fullbright CommissionUNSPECIFIED
Issue or Number:24
Record Number:CaltechAUTHORS:20160823-093537115
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Official Citation:Ground- and Excited-State Reactions of Norbornene and Isomers: A CASSCF Study and Comparison with Femtosecond Experiments Sarah Wilsey, K. N. Houk, and A. H. Zewail Journal of the American Chemical Society 1999 121 (24), 5772-5786 DOI: 10.1021/ja983480r
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69845
Deposited By: Ruth Sustaita
Deposited On:23 Aug 2016 18:53
Last Modified:11 Nov 2021 04:20

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