Probing Radical Addition to 1-Phosphabutadienes by Employing Muonium as a "Light Isotope" of Hydrogen.

Understanding free radical addition to multiple bonds is important to elucidating the mechanistic details of addition polymerization reactions, albeit the fleeting radical intermediates are very difficult to detect by conventional methodologies. Muon spin spectroscopy (μSR) is a highly sensitive method that can detect radical species at 10 spins (cf. EPR: 10 spins, NMR: 10 spins).

The Reaction of Muonium with Hydrogen Peroxide in Aqueous Solution.

Rate constants for the reactions of muonium (Mu) (the ultralight isotope of the hydrogen atom) with H O in H O and D O in D O have been determined at various temperatures and pH (pD) values. The data are consistent with the three reactions: , , and the equivalent for the deuterated entities. A significant positive H/D isotope effect was found for the undissociated peroxide, while for the anions the effect was negligible or slightly in the opposite direction.

Free Radicals Formed by H Atom Addition to Allenes as Determined by Muon Spin Spectroscopy.

Allyl and vinyl radicals are important intermediates in diverse areas of chemistry, ranging from combustion to synthesis. However, questions remain about the competitive formation of these radicals from allenes. Here, we present a study of prototypical allyl and vinyl radicals formed by H atom addition to allenes.

Free Radical Chemistry of Phosphasilenes.

Understanding the characteristics of radicals formed from silicon-containing heavy analogues of alkenes is of great importance for their application in radical polymerization. Steric and electronic substituent effects in compounds such as phosphasilenes not only stabilize the Si=P double bond, but also influence the structure and species of the formed radicals. Herein we report our first investigations of radicals derived from phosphasilenes with Mes, Tip, Dur, and NMe substituents on the P atom, using muon spin spectroscopy and DFT calculations.

Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues.

Muonium (Mu), an H atom analogue, is employed to probe the addition of free radicals to the P=C bond of a phosphaalkene. Specifically, two unprecedented muoniated free radicals, MesP -CMu(Me) (1 a, minor product) and MesPMu-C Me (1 b, major product), were detected by muon spin spectroscopy (μSR) when a solution of MesP=CMe (1: Mes=2,4,6-trimethylphenyl) was exposed to a beam of positive muons (μ ). The μ serves as a source of Mu (that is, Mu=μ +e ).