Question

Which of the following correctly ranks the cycloalkanes in order of increasing ring strain per methylene?cyclohexane < cyclobutane < cyclopentane < cyclopropanecyclopropane < cyclopentane < cyclobutane < cyclohexanecyclopentane < cyclopropane < cyclobutane < cyclohexanecyclohexane < cyclopentane < cyclobutane cyclopropanecyclopropane < cyclobutane < cyclohexane < cyclopentane

Answer 1

The correct rank of cycloalkanes in order of increasing ring strain per methylene is:

Cyclohexane < Cyclopentane < Cyclobutane < Cyclopropane.

Ring strain occurs because carbons in cycloalkanes are sp3 hybridized, so their expected ideal bond is of 109.5°. Therefore in cycloalcanes with angles smaller than 109.5° the potential energy increases.

The correct order is the given above because the shape of the molecules determines the angle between the carbon atoms and the ring strain resulting grows from cyclohexane to cyclopropane.