Theoretical study of the internal rotation of cubylcubane and cubylcubane difluoride

We present a theoretical study of the internal rotation of cubylcubane (CCB) (C8H7)2 and cubylcubane difluoride (CCB-2F) (C7H6F)2. Calculations at the ab initio HF//6-311G**, MP2 and DFT/B3LYP levels show that CCB presents an energy barrier at α=0° of about 4.8 kcal/mol, the addition of two fluorine atoms on each cage leads to a potential profile presenting two maxima, at α=0° (8.6 kcal/mol) and 120° (4.6 kcal/mol). The potential barriers hindering the internal rotation have been characterized by partitioning the potential function in terms of contributions due to interactions through bond and through space. It is found that the potential barriers are basically due to the through space electrostatic interactions.