Another consequence of the different metrics / greater in plane turn in 1-Br relative to [5]helicene C is a greater barrier to racemization. The BN- [5]helicenes 1-H and 1-Mes were calculated to have higher barriers to P -M interconversion by ca. 1.5 kcal mol -1 than C and a 7-mesityl derivative. [5]helicene has been determined previously to have a barrier to racemization of ca. 24 kcal mol -1 . It is also important to note that 1-H and 1-Mes have effectively identical calculated barriers to racemization (E = 0.2 kcal mol -1 ) confirming that there is minimal effect when changing a substituent on the outer helix.