Q. Considering that the angles of a regular pentagon are 108º, why is cyclopentane not planar?

1. all the carbons are sp2 hybridized, so there is considerable angle strain.
2. The C-C bonds are formed by overlap of p-orbitals, so the 90º angle results in large angle strain.
3. The cyclic overlap of bonding orbitals results in anti-aromaticity destabilization
4. The five C-C bonds have eclipsing strain