Ab initio calculations of the barrier to CF2 rotation in 1,1,3,3-tetrafluoropropenyl radical

Ab initio calculations have been performed with the 6-31G * basis set on the barrier to rotation of a CH 2 group in the propenyl radical (1) and the barrier to rotation of a CF 2 group in the title radical (2). Unlike the case in 1, pyramidalization of the terminal carbons is predicted at the equilibrium geometry (2a) of 2 at some levels of theory; and at all levels of theory substantial pyramidalization of the rotated carbon in the transition state (2b) is computed to be quite favorable energetically. The calculations reveal that CF 2 group pyramidalization in 2b is, in fact, the major factor responsible for the barrier to rotation about a C-C bond being lower in 2 than in 1