Ab initio and DFT Study for the Internal Rotations of Cyclopropyldifluoroborane Molecule

The equilibrium structures, relative energies and NBO analyses for the possible conformations and transition states which can exist on the internal rotation of CPDFB and CPCFB molecules have been investigated using DFT and ab initio methods with various basis sets. The interaction between bonding orbital (sigma(C-1-C-3, C-2-C-3)) and antibonding orbital (n*(B-9) and sigma*(B-9-Cl-11)) was the main characteristic hyperconjugation in both molecules. In addition, the stabilization energy of CPDFB was 6.63 kcal/mol and that of CPCFB was 6.97(E-form)/6.79(Z-form) kcal/mol for each conformation. The rotational barriers by internal rotation of BF2-and BFCl-functional groups were evaluated to be 5.3 similar to 6.7 kcal/mol and 5.7 similar to 6.5 kcal/mol respectively, which showed good agreement with the experimental values reported by previous dynamic NMR study. Finally, Z-form was more stable than E-form by 0.2 kcal/mol in CPCFB molecule and therefore Z-form was confirmed as global minimum.