Wlodek, Stanislaw

Muonium adds to allyl chloride, CH2=CHCH2Cl, to form two radicals: MuCH2CHCH2Cl (main product) and CH2CHMuCH2Cl (minor product). Both radicals were fully characterized byμSR andμLCR. In the main product, the LCR lines due to the35Cl and37Cl nuclei were observed. Also, the temperature dependence of various hyperfine coupling constants (hfc) indicates that both Mu and Cl eclipse the unpaired electronp 2-orbital in the minimum energy conformation. For the fragment-CH2Cl, the presence of Mu in theβ′-position is found to affect significantly the hfc of Cl in theβ-position; an internal rotational barrier of 12 kJ mol−1 was estimated using a simpleV 2 torsional potential.

Muonium adds to the unsaturated bond in 1,3-dithiolane-2-thione or -2-selenone to form a chalcogen-centered radical. The muon hyperfine coupling constants (hfc) were measured for both compounds over a range of temperatures. In solution, the temperature dependence of the muon hfc indicates that for the thiyl radical the preferred conformation corresponds to the muon eclipsing the unpaired electronp z-orbital, while there is practically free rotation in the case of the selenenyl radical in the temperature range studied. In pure thione the hfc values show a remarkable discontinuity at the melting point. The two radical signals seen in the solid are interpreted as due to the presence of two dominant crystal orientations in the samples studied. In pure selenone data were obtained only in the solid. For both systems, the solid phase results show that interaction between the muon and the unpaired electron spin is enhanced compared to the liquid phase and/or the solution.

Four of the five possible isomeric C70Mu radicals have been detected by transversefieldμSR in a C70 powder sample at 298 K. Their assignment is based on the results of semi-empirical MNDO calculations. There are significant changes in intensity and lineshape of the signals at low temperature. The first μSR spectrum of a fullerenyl radical in solution has been obtained.

Reported here is the first observation of anα-Muonium-substituted methyl radical. The key to the success of this experiment was the use of a more stable precursor, trimethylsilyldiazomethane, in lieu of the prototypical diazomethane. The radical, CHMuSi(CH3)3 was observed by TF-μSR, with Aμ=187.6(2) MHz. This result is compared to literature values for the proton analogue and the isotope effect is discussed.