A level-crossing-resonance study of muonated free-radical formation in solutions of acetone in hexane, water and dilute micelles

Venkateswaran, Krishnan; Kiefl, R. F.; Barnabas, Mary V.; Stadlbauer, John M.; Ng, B. W.; Wu, Zhennan; Walker, David C.

doi:10.1016/0009-2614(88)80009-5

Cited by 23 publications

(12 citation statements)

References 12 publications

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“…For a given resonance, PR ci and all yields for a given resonance can be normalized by comparison with neat acetone using the published yield of 0.41 (4). Table 1 shows the Mu-radical yields obtained at three concentrations of acetone (100, 27, and 10 mM) for surfactant additions up through the CMC to micelle concentrations of 9 mM.…”

Section: P"mentioning

confidence: 99%

“…It was used here to put all P, values on an absolute basis -as a normalizing factor for the actual asymmetry of the apparatus (As, in eq. [4]). …”

Section: P"mentioning

confidence: 99%

“…It has also been well characterized by level-crossing resonance spectroscopy (pLCR) in the neat liquid state (7) and in dilute solutions in hexane and in water (4). It has an isotropic muon hyperfine coupling constant (Ap) of 26.1 MHz in neat acetone.…”

Section: Introductionmentioning

confidence: 99%

“…A,, is largest in water (3), intermediate in neat liquid acetone (2), and smallest in hydrocarbons (4). The increase from neat acetone to water has been ascribed to "muonium bonding," isotopomeric hydrogen bonding (3).…”

Section: Introductionmentioning

confidence: 99%

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Micelle-induced change of mechanism in the reaction of muonium with acetone

Stadlbauer¹,

Venkateswaran²,

Gillis³

et al. 1996

Can. J. Chem.

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Muonium atoms add to the 0 atom of the carbonyl group of acetone to give the muonated free radical (CH~)~C-O-MU when the reaction takes place in water or hydrocarbons, but not when the acetone is localized in micelles. Micelles have no effect on the formation of muonated cyclohexadienyl radicals when muonium reacts with benzene under similar conditions. The addition reaction with acetone appears to have been subsumed by a faster alternative reaction in the micellar environment. Evidence is presented for this interpretation rather than for an inhibition of the radical or for a shift in the muon level-crossing resonance spectrum with hydrogen (muonium) bonding, though major shifts are seen for the spectrum of this radical in pure solvents of widely different dielectric constant. It is suggested that muonium's "abstraction" reaction takes over in micelles because significant micelle-induced enhancement effects were previously observed in that type of reaction. The data are consistent with a rate constant for the abstraction reaction of muonium with acetone in micelles of >6 x lo8 M-' SKI.Key words: muonium, kinetic isotope effects, micelle enhancement, HMu-addition, H M u abstraction.RCsumC : Lorsqu'on opkre en solution dans I'eau ou dans les hydrocarbures, les atomes de muonium s'ajoutent h I'atome d'oxygkne du groupe carbonyle de l'acitone pour conduire h un radical muone (CH~)~C-O-MU; ce n'est toutefois pas le cas lorsque l'acitone est localisie dans des micelles. Les micelles n'ont aucun effet sur la formation de radicaux cyclohexadiinyles muonts lorsqu'on fait riagir des atomes de muonium avec le benzkne, dans des conditions semblables. I1 semble que, dans un environnement micellaire, la riaction d'addition sur l'acitone est dipassi par une autre riaction plus rapide. On prisente des rLsultats confortant cette interpretation plut6t que celle faisant appel h une inhibition du radical ou h un diplacement du spectre de risonance de croisement au niveau du muon avec une liaison hydrogkne (muonium); toutefois, on observe des diplacements pour les spectres de ce radical dans des solvants purs de constantes diilectriques fort diffirentes. On suggkre que la riaction d'<(enlkvementn des muonium se produit dans des micelles en raison des effets de rehaussement induit par les micelles qui ont it6 observis antirieurement dans ce type de riaction. Les donnies sont en accord avec une constante de vitesse, pour la riaction d'enlkvement du muonium avec l'acitone dans les micelles, qui serait supirieure h 6 x loX M-' s-I.

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Section: P"mentioning

confidence: 99%

“…It was used here to put all P, values on an absolute basis -as a normalizing factor for the actual asymmetry of the apparatus (As, in eq. [4]). …”

Section: P"mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Micelle-induced change of mechanism in the reaction of muonium with acetone

Stadlbauer¹,

Venkateswaran²,

Gillis³

et al. 1996

Can. J. Chem.

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“…[3] to be 0.16 (22) (equal to the scavengable muonium yield in water for those conditions). In experiments with 0.01 M acetone, the yield was found to be smaller still (0.11) (22), as given in Table 3. This difference is due to significant radioactive decay of the muon in muonium prior to it being scavenged by acetone, particularly at the lowest concentration.…”

Section: (B) Muonated Free Radicals In Acetonementioning

confidence: 99%

Isotope effects in solution: contrasts between muonium and hydrogen in reactions with acetone

Walker¹

1990

Can. J. Chem.

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Munoniurn atoms are hydrogen isotopes with positive muons rather than protons, deuterons, or tritons as nuclei. Thus, they have one ninth the mass of 'H, and microsecond lifetimes. By using nuclear physics counting techniques, rnuoniurn can be studied in a wide variety of media and its chemical and physical properties used to appraise hydrogen. Results are described for the interaction of muoniurn with acetone, showing two types of kinetic isotope effects, formation of free radicals, evidence for intermolecular "rnuoniurn bonding", and rnicelle-induced enhancements of reaction rate constants.

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