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, MuCH2-.CH-CH2Cl. 2-methyl-3-chloropropene yields only the tertiary radical, MuCH2-.C(CH3)-CH2Cl. These three chloroalkyl radicals have been characterized by μSR and μLCR, 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 variation of the hfcs has been analyzed to obtain estimates of the barrier to internal rotation about the Cα-Cβ axis for various alkyl groups, and also their minimum energy conformations, i.e. their orientations with respect to the axis of the 2pz orbital of the unpaired electron. The tertiary radical is particularly interesting because all three methyl-like groups, -CH3,-CH2Cl and -CH2Mu, are represented. The results can be compared to electron spin resonance data for analogous radicals, to provide information on the effects of Mu substitution for H