Angle Strain - Examples

Examples

In cycloalkanes, each carbon is bonded nonpolar covalently to two carbons and two hydrogen. The carbons have sp3 hybrization and should have ideal bond angles of 109.5°. Due to the limitations of cyclic structure, however, the ideal angle is only achieved in a six carbon ring — cyclohexane in chair conformation. For other cycloalkanes, the bond angles deviate from ideal. In cyclopropanes (3 carbons) and cyclobutanes (4 carbons) the C-C bonds are 60° and ~90° respectively.

Examples of molecules with angle strain include cycloalkanes, cyclophanes, platonic hydrocarbons and pyramidal alkenes.

Some specific examples are:

• cyclopropane, C₃H₆ — the C-C-C bond angles are 60° whereas tetrahedral 109.5° bond angles are expected. The intense angle strain leads to nonlinear orbital overlap of its sp3 orbitals. Because of the bond's instability, cyclopropane is more reactive than other alkanes. Since any three points make a plane and cyclopropane has only three carbons, cyclopropane is planar. The H-C-H bond angle is 115° whereas 106° is expected as in the CH₂ groups of propane.
• cyclobutane, C₄H₈ — if it was completely square planar its bond angles would be 90° whereas tetrahedral 109.5° bond angles are expected. However, the actual C-C-C bond angle is 88° because it has a slightly folded form to relieve some torsional strain at the expense of slightly more angle strain. The high strain energy of cyclobutane is primarily from angle strain.
• cyclopentane, C₅H₁₀ — if it was completely rectangular planar pentagon its bond angles would be 108° whereas tetrahedral 109.5° bond angles are expected. However, it has an unfixed puckered shape that undulates up and down. The unstable half-chair conformation has angle strain in the C-C-C angles which range from 109.86° to 119.07°.
• ethylene oxide, CH₂OCH₂
• cubane, C₈H₈