The meta photocycloaddition of benzene to ethylene: ab initio calculation of a symmetric pathway

Stehouwer, A; Hart, Johanna A. van der; Mulder, J. J. C.; Cornelisse, J.

doi:10.1016/0166-1280(92)87053-3

Cited by 4 publications

(2 citation statements)

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“…Cornelisse et al discussed the three modes of addition using quantum chemical methods as well as qualitative molecular orbital diagrams. 16,22,32,33 Some 16 years ago we performed a CASSCF study with MMVB dynamics for S 1 benzene with ethylene. 29 These computations located an isolated conical intersection that was suggested to be an important feature in the mechanism.…”

Section: ■ Introductionmentioning

confidence: 99%

“…These selectivities were also found to be influenced by the photoinduced charge transfer and, in addition to the exciplex, dipolar intermediates were considered in order to explain the high regioselectivities of photocycloadditions with donor-and acceptor-substituted arenes. Cornelisse et al discussed the three modes of addition using quantum chemical methods as well as qualitative molecular orbital diagrams 16,22,32,33 .…”

Section: Scheme 1mentioning

confidence: 99%

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How the Conical Intersection Seam Controls Chemical Selectivity in the Photocycloaddition of Ethylene and Benzene

et al. 2012

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The photocycloaddition reaction of benzene with ethylene has been studied at the CASSCF level, including the characterization of an extended conical intersection seam. We show that the regioselectivity is, in part, controlled by this extended conical intersection seam and that the shape of the conical intersection seam can be understood in terms of simple VB arguments. Further, the shape and energetics of the asynchronous segment of the conical intersection seam, suggests that 1,2 (ortho) and 1,3 (meta) will be the preferred regioselectivities with similar weight. The 1,4 (para) point on the conical intersection is higher in energy and corresponds to a local maximum on the seam. VB analysis shows that the pairs of VB structures along this asynchronous seam are the same and thus the shape will be determined mainly by steric effects. Synchronous structures on the seam are higher in energy and belong to a different branch of the seam separated by a saddle point on the seam. On S 1 we have documented three mechanistic pathways corresponding to transition states (with low barriers) between the reactants and the conical intersection seam: a mixed asynchronous/synchronous [1,2] ortho path, an asynchronous [1,3] meta path and a synchronous [1,3] meta path. 2 I IntroductionIn general, a photochemical reaction path has two branches: a branch on the excited state and a branch on the ground state. The two branches are connected at a point where the potential energy surfaces become degenerate known as a conical intersection (CI) [1][2][3][4][5][6][7] . However, a conical intersection is not an isolated point, but a collection of points, which we will refer to as a conical intersection "seam" 1,[8][9][10] . In this work we shall explore this feature in some depth for the case of the photochemical reactivity of ethylene and benzene. In the photocycloaddition of an arene and an alkene there are several possible regioselectivities (Scheme I). We will show that this regioselectivity is in part controlled by such an extended conical intersection seam.Experimental Background: Cycloadditions with alkenes are important and characteristic photochemical reactions of aromatic compounds. The prototype example of such a photocycloaddition is the reaction of benzene with ethylene [11][12][13][14][15][16][17][18][19][20][21][22] . Three cycloaddition modes (regioselectivity) can be distinguished (See Scheme 1): ortho-cycloaddition [1,2], meta-cycloaddition [1,3], and para-cycloaddition [1,4], and many applications of these reactions in organic synthesis have been described, as they afford the possibility to obtain polycyclic compounds in one step, which is important in the design of more complex molecular frameworks. Scheme 1 3The photocycloaddition reactions of arenes with alkenes have been extensively studied in order to rationalize the formation of the three possible cycloaddition products 11,16 . The meta-cycloaddition mode ([1,3] in our simplified notation) has been applied most extensively and is used as an important step in ...

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Section: ■ Introductionmentioning

confidence: 99%

Section: Scheme 1mentioning

confidence: 99%