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Cycloalkanes: Structural Variety

Cycloalkanes: Cyclopropane

3D Model
Bond lengths and bond angles of cyclopropane

Cyclopropane exists in the form of a planar, equilateral triangle, a regular polygon with the C-C-C angles measuring 60° which is a clear deviation from a tetrahedral angle of 109.5°. Additionally, all hydrogen atoms are eclipsed resulting in greater instability and a more positive enthalpy than is observed for other cycloalkanes. Because of the bent bonds in cyclopropane, the orbitals assume an angle of 104° which allows for sufficient overlap to form a bond. This is the reason that such a deformed bond structure is even possible.

The C-C bonds in cyclopropane are relatively weak because of the ring strain. Ring opening requires an energy of only 272 kJmol-1 as compared to 377 kJmol-1 for cleavage of the C-C bond in ethane. The low energy required accounts for unusual reactions of cyclopropane.

Rearrangement to propene
Hydrogenation to propane
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