Planar cyclopentane has virtually no angle strain but an immense amount of torsional strain. To reduce torsional strain, cyclopentane addops a non-planar conformation even though it slightly increases angle strain. ... The envelope removes torsional strain along the sides and flap of the envelope.
Is cyclopentane a planar?
A cyclopentane ring can exist in a planar conformation with little angle strain because the internal angle of a pentagon is 108o, quite close to the tetrahedral angle of 109.5o. ... Cyclopentane is a twisted ring in the form of an “envelope” so that one of the carbon atoms is out of the plane of the ring.
Why is cyclohexane not planar?
Short answer: Benzene is planar because its carbon atoms are sp2 hybridized, and cyclohexane is nonplanar because its carbon atoms are sp3 hybridized.
