Temperature Dependence of Spin—Spin Splitting in the Hindered Rotator CHCl2–CF2Cl

The effective H1–F19 spin coupling in CHCl2–CClF2 changes from 5.40 cps at —40°C to 5.60 cps at +100°C. This variation has been analyzed to obtain the difference in potential energy between the two energetically distinct staggered rotational isomers. The result is that the isomer possessing a plane of symmetry is either 2.0 kcal/mole more stable or 1.8 kcal/mole less stable than the other pair. The consequences of this result for the theory of spin—spin splitting are briefly discussed.