INTRAMOLECULAR MOTION AND ISOTOPE EFFECTS IN MUONIUM-SUBSTITUTED CHLOROALKYL RADICALS

Muon irradiation of pure liquid 3-chloropropene, CH2=CH-CH2Cl, yields a primary radical, CH2-CHMu-CH2Cl, and a secondary radical, MuCH(2)-CH -CH2Cl. 2-methyl 3-chloropropene yields only the tertiary radical, MuC H(2)-C(CH3)-CH2Cl. These three chloroalkyl radicals have been characte rized by mu SR and mu LCR, and the hyperfine coupling constants (hfcs) have been determined over a range of temperatures, either in the pure liquid precursor or in concentrated solution. The temperature variati on of the hfcs has been analyzed to obtain estimates of the barrier to internal rotation about the C-alpha-C-beta axis for various alkyl gro ups, and also their minimum energy conformations, i.e. their orientati ons with respect to the axis of the 2p(z) orbital of the unpaired elec tron. The tertiary radical is particularly interesting because all thr ee methyl-like groups, -CH3, -CH2Cl and -CH(2)Mu, are represented. The results can be compared to electron spin resonance data for analogous radicals, to provide information on the effects of Mu substitution fo r H.