Table 5.5 Central Atom s and p Orbital Transformations under Different Symmetries. |

Spiroconjugation [6] is claimed to occur in the electronic structure of the polyspiroquinoid chain. [1] This type of through-space interaction can be considered in terms of 4 p atomic orbitals held spiro to each other about a tetrahedral C atom (see Fig. 3). These four orbitals interact to form 4 combinations of differeing symmetry with respect to the two perpendicular mirror planes dividing the tetrahedral C atom. One combination is symmetric under reflection in each mirror plane, labeled (SS), and there are also (SA), (AS) and (AA) combinations. The (AA) combination is shown, it is of the proper symmetry for a bonding spiro-type interaction. [Pg.5]

Fig. 14.21. Cyclization of the cis-butadiene. (a) Start from the top coniotation (leftward) and disrotation (rightward) lead in general to different products, but only one of these transformation is symmetry allowed, (b) The doubly occupied n orbitals of the butadiene (p (HOMO-1) and (HOMO), (c) The transformation of >P2 under the conrotation and disrotation. The conrotation is symmetry-allowed, and the disrotation is symmetry-forbidden. |

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