ORBITAL AND STATE CORRELATION DIAGRAMS

The MOs and electronic states of carbene have been discussed in Chapter 7. The orbital and state correlation diagrams for addition of CH2 to ethylene is shown in Figure 14.9. The Walsh bonding picture for the MOs of cyclopropane requires that the and a MOs of the ethylene also be included in the diagram. The a2 and least-motion pathway preserves a vertical plane of symmetry (as well as the other elements of the C2v point group), and the... 

Decide on the basis of orbital and state correlation diagrams whether or not the reaction is photolytically allowed. 

From the orbital correlation diagram derived by Bryce-Smith [38], it was deduced that the ortho cycloaddition is forbidden from the lowest excited singlet state of benzene and the ground state of ethene. Van der Hart et al. [189] have constructed molecular orbital and state correlation diagrams for the ortho photocycloaddition of benzene to ethene. The molecular orbital correlation diagram differs from that given by Bryce-Smith, because natural correlations have been used. From a topological point of view, it seems less desirable to correlate the tt... 

Three levels of explanation have been advanced to account for the patterns of reactivity encompassed by the Woodward-Hoffmann rules. The first draws attention to the frequency with which pericyclic reactions have a transition structure with (An + 2) electrons in a cyclic conjugated system, which can be seen as being aromatic. The second makes the point that the interaction of the appropriate frontier orbitals matches the observed stereochemistry. The third is to use orbital and state correlation diagrams in a compellingly satisfying treatment for those cases with identifiable elements of symmetry. Molecular orbital theory is the basis for all these related explanations. 

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