Although the activation energy barrier to enantiomer interconversion for [4]helicene is small at ≈ 17 kJ mol -1 , 61 the racemic structure is only 1.66 kJ mol -1 lower in energy than the enantiopure structure; thus, the racemic structure is unlikely to form from an enantiopure solution, resulting in the crystallization of the enantiopure polymorph.