Organic Lecture 6: Ring Strain

We'll start the new year off with a short lesson, partly because I'm extremely hung over.

Ring strain arises when bond angles between ring atoms deviate from the ideal angle predicted by hybridization of the atoms.

Cyclopropane is very strained because the carbon-carbon bond angles are 60 degrees rather than the idealized 109 degrees for sp3 hybridized carbons.

Cyclobutane has carbon-carbon bond angles of 88 degrees.

**The deviation of the bond angles from the normal tetrahedral 109 degrees causes cyclopropane and cyclobutane to be unstable. The strain weakens the carbon-carbon bonds and increases the reactivity of them (C-C bonds in these highly strained cyclic molecules are significantly more reactive). Because of this, both cyclopronane and cyclobutane can undergo hydrogenation. However, cyclopentane and cyclohexane are more stable because they have near tetrahedral bond angles due to the conformations they adopt.