Molecular gymnastics in 2+2 cycloadditions. Two different moves compared.

The previous post showed how the 2+2 cycloaddition of an alkene could occur by a sort of sideways insinuation of the bonds. I have also shown how the same reaction can occur with a dramatic rotation of one of the double bonds. This post compares the two moves side by side.

0.0 5.3 kcal/mol

The forbidden dance

The allowed dance.

As is sometimes the case in real life, the forbidden option has the lower activation barrier!

Henry Rzepa

Henry Rzepa is Emeritus Professor of Computational Chemistry at Imperial College London.

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