Some data correlated by the I-strain concept

There have been a substantial number of cases of misinterpretation and misapplication of this general principle. Specifically, it is incorrect to conclude that double bonds prefer to be exocyclic in five-membered rings and endocyclic in six-membered rings. For example, both methylenecyclopentane and methylenecyc-lohexane are less stable than the endocyclic isomers  

Alkenes exhibit large strain effects when factors of molecular geometry do not permit all the bonds to the two -hybridized carbons to be coplanar. An example that illustrates the twisting of an olefinic 7r-system can be found in trans-cycloheptene  

The geometry of bicyclic rings can also cause distortion of the coplanarity of olefinic systems. One example of this is bicyclo[2.2.1]hept-l-ene  

Attempts to construct a model of this molecule will show that the geometry of the bicyclic system does not permit coplanarity of the substituents bonded to the 

With unhindered ketones, steric repulsions between the substrate and a small reagent become less important, and other considerations come into play. The reduction of 4-r-butylcyclohexanone with sodium borohydride or lithium aluminum hydride gives predominantly the product of axial hydride transfer, the equatorial alcohol /ra s-4-r-butylcyclohexanol 

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Scheme 3.3. Some Data Correlated by the I-Strain Concept"...

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