Photochemical valence isomerization to high energy products – Bicyclobutanes and Oxabicyclobutanes

The photochemical valence isomerization of 1,3-butadienes give bicyclobutane 1(X=CH2). The stereochemistry of these strained products in substituted derivatives suggest a double disrotatory ring cyclization originating from the second excited state of the diene.. The oxygen analog valence isomerization from acrolein has not been reported nor its product, oxabicyclobutane 1(X=O). DFT computations for both bicyclics showed a large basicity for the carbon analog exceeding that of the oxygen analog. The strain energy for oxabicyclobutane exceeds that for bicyclobutane. The validity of the computational method is seen from the congruence between experimental and computational values of the structural and thermochemical parameters.

Audience take-away:

 

• Audience will learn about principles of photochemistry.
• Introduction of strain and determination of strain energy.
• Definition of proton affinity and basicity.
• Illustration of valence isomerizations.