Cyclobutane bond angle deformation

Stability. The four-membered ring in the diazabiphenylene series of compounds is strained due to bond angle deformation . The conventional ring strain energy for cyclobutane is 111 kj moP alkyl substituents stabilize the ring by only a few kilojoules per mole. 

The strain energies of cyclopropane (26.5 kcaFmol) and cyclobutane (26 kcal/ mol) are nearly the same despite the apparent much greater bond angle deformation with the former. One reason is that the weak C—C bonds in cyclopropane are compensated in part by the stronger C—H bonds. The increased strength results from the greater s character, and it is known that C—H bond strengths increase with... 

Many of the unique properties of cyclopropanes, and to a lesser extent, cyclobutanes, are derived from the formation of bent bonds. They may act in a fashion similar to 7r-bonds in interacting with electron-deficient centers, and are more easily cleaved thermally via electrophilic attack than are ordinary C-C bonds. The strain energy associated with bond angle deformation is also an important quantity, especially when considering thermal reactions. 

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