Muonic radicals

Multimetallic fullerene adducts, 44 24, 26-28 Multinuclear metalloenzymes, 44 247-258 nt Multiple bonds, 33 260 structure of and proofs for, 33 256 Muonic radical, formation and reactions of, 28 122-130... 

Before the first muonic radicals were observed in 1978 by Roduner et al. (122), rate constants had been measured for the addition of Mu to unsaturated compounds in aqueous solution (Table XI). If k Jku is larger than 3, tunneling may be important, since otherwise differences in the vibrational zero-point energy in the transition state can decrease this ratio (128). In the case of maleic acid, the Arrhenius parameters were determined as A = (2.3 0.2) x 1013 AT-1 sec-1 and E = 18.8 1.7 kJ mol-1. Rate constants were also measured for addition to the CN triple bond (127). 

The discovery of muonic radicals in 1978 by Roduner opened up a broad field of interesting experiments. Aromatic substitution is normally studied by the measurement of the yields of stable products. This includes not only the site of addition of the reactant, but also the splitting off of the atom that is substituted. With the MuSR technique only the first step is studied exclusively. Another development concerns the measurements of the reactions of muonic radicals dimerization, ring opening, and ring closure. The observations of different reaction rates of the three isomeric muonic cyclohexadienyl radicals from anisole with quinones also opens a new field of investigation. 

Figure 15. /iSR Fourier power spectra at several magnetic fields for the muonic radical 2,3-dimethyl-2-butene. (From Ref. 23.)... 

In strong magnetic fields B 0.1 T), several muonic radicals were observed because of their characteristic split muonium frequencies. 

The measured amplitudes are usually scaled to give fractional diamagnetic, muonium, and muonic radical polarizations, directly related to the formation probabilities of the species. 

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