Question

Rotation occurs freely around what hybridization?

Answer 1

Any and all hybridizations.

All hybrid orbitals can only make `sigma` bonds (i.e. a single bond, or the first bond in a double or triple bond). These `sigma` bonds are formed from atomic orbitals that are infinitely symmetric about the internuclear axis. That means a rotation about the internuclear axis by an infinitely small angle returns the same molecule back.

Therefore, any `sigma` bond can rotate without breaking the symmetry of the molecule (the symmetry must be maintained in order for the bond to stay intact).

Hence, any bonds made with a hybrid orbital can rotate freely.