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Quantum-chemical studies of double bond pyramidalization of sesquinorbornenes and related strained polycyclic molecules

In strained olefins of low symmetry, the two carbon atoms of the double bond and their four attached substituents tend to adopt a non-planar conformation and are termed pyramidal olefins. Norbornene and its derivatives, especially those resulting from syn fusion of another norbornyl nucleus, e.g., syn-sesquinorbornene, have double bonds that are considerably pyramidalized in the endo direction. In this chapter, an review on quantum-chemical studies of double bond pyramidalization of sesquinorbornenes and related strained polycyclic molecules (such as nor-, homo- and bishomo- sesquinorbornenes) is presented. The heterosesquinorbornenes possessing heteroatoms, particularly these at the 7-position of norbornene moiety are also included (O, N, B, Al, S, Si, Ge, Sn, P, As) and their influence on the extent of double bond pyramidalization. The suitability of various quantum-chemical methods to correctly predict the extent of pyramidalization of these systems has been evaluated by a comparison of performances of Hartree-Fock, MP2, DFT and MCSCF methods, employing basis sets of different sizes with experimentally available data. For a precise description of the double-bond folding in pyramidalized olefins the inclusion of valence electron correlation at the DFT or MP2 levels of theory is required.

computational chemistry ; sesquinrbornenes ; pyramidalization

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