Rearrangement, -sigmatropic orbital description

It is possible to give a frontier orbital description of a [3,3] -sigmatropic rearrangement but this is not a very satisfactory treatment because two reagents are not recognizing each other across space as they were in cycloadditions. There are three components in these reactions—two nonconjugated K bonds that do have to overlap across space and a O bond in the chain joining the two k bonds. 

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