Revisiting the racemization mechanism of helicenes.

Herein we propose a general mechanism for the racemization of [n]helicenes up to n = 24. It is a concerted process for n = 4-7, but a multi-step mechanism is followed for n≥ 8, involving 2n- 14 intermediates. The changes in the barriers are a delicate consequence of the steric hindrance and the π-interactions.