Competition between benzene and styrene in forming radicals under different solvent conditions observed by muon level crossing resonance

Abstract

The muon level-crossing-resonance technique has been used to resolve major discrepancies that exist in muon-spin-resonance studies (both free-radical formation and muonium decay rates) in the competition between benzene and styrene. The results, obtained for ∼30 mM solutions in ethanol and for 2.5 mM aqueous micelles solutions, show that muonium atoms (Mu) react 8 (±2) times faster with styrene than with benzene. In the above cases thermalized Mu is unquestionably the reactive species, which is known to show nucleophilic intra-molecular selectivity in the case of styrene. But a similar value, 9 (±2), was also obtained for undiluted mixtures of liquid benzene and styrene (neat mixture) — where the precursor might have been ‘hot Mu’ (which should display weaker selectivity than Mu) or cations derived fromμ ⁺ (which should show higher selectivity). These results support the view that thermalized Mu is the predominant reactive species in liquid benzene and styrene.