13C hyperfine coupling and structure of the .CHCl2 radical in CH2Cl2 crystal by ESR

Measurement of the 13C hyperfine coupling constant of .CHCl2 in single crystal CH2Cl2 at 77 K leads to the conclusion that the radical converts between two equivalent pyramidal structures at a rate significantly higher than 109Hz. The anisotropy of the g-factor and the 1H, 35Cl and 13C hyperfine couplings is consistent with an average planar structure. The conclusion is supported by ab initio calculations which show that the barrier for interconversion corresponds to a rate of the order 1013Hz. A similar behaviour is predicted for .CH2Cl. (Auth.)