Benzvalene correlation diagram

Figure 14.7. Orbital correlation diagram for the thermal rearrangement of benzvalene to benzene. A C2 axis of symmetry is preserved.

The fact that the benzvalene-benzene interconversion is allowed in global symmetry led Mulder [31] to conclude that the Woodward-Hoffmann Rules that were designed to deduce stereochemistry, should be distinguished from the use of orbital correlation diagrams, and that correlation of the occupied orbitals of the reactant and product is no guarantee that the reaction will not have a high activation energy. 

The situations of this type are not, fortunately, very frequent for thermal reactions (e.g. the benzene to benzvalene or cyclooktatetraene to cubane transformations), but in photochemistry are quite common. For the analysis of these reactions the concept of the so-called natural correlation diagrams was introduced [31]. The construction of these diagrams is not, however, so straightforward as the construction of the... 

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