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 present s an energy barrier at alpha = 0 degrees of about 4.8 kcal/mol, the additio n of two fluorine atoms on each cage leads to a potential profile presentin g two maxima, at alpha = 0 degrees (8.6 kcal/mol) and 120 degrees (4.6 kcal /mol). The potential barriers hindering the internal rotation have been cha racterized by partitioning the potential function in terms of contributions due to interactions through bond and through space. It is found that the p otential barriers are basically due to the through space electrostatic inte ractions. (C) 2001 Elsevier Science B.V. All rights reserved.