The Mechanism of Decomposition of Azo Compounds. II. Cage Effects in the Decomposition of α,α-Azoisobutyronitrile and Related Compounds

Hammond, George S.; Wu, Chin-Hua S.; Trapp, Orlin D.; Warkentin, John; Keys, Richard T.

doi:10.1021/ja01505a026

Cited by 84 publications

(20 citation statements)

References 3 publications

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“…Geminate cage pairs are born with the proper orientation, and they have no time to rotate in the cage; therefore, recombination is expedited. In contrast, collisional cage pairs are more likely to form with improper orbital orientation and therefore combination is less likely …”

Section: Resultsmentioning

confidence: 99%

Solvent Cage Effects: A Comparison of Geminate and Nongeminate Radical Cage Pair Combination Efficiencies

Barry

Tyler

2020

Inorg. Chem.

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This study measured and compared the combination efficiencies (F cP ) of geminate radical cage pairs to nongeminate (collisional) radical cage pairs (F c ′). For the [Cp′(CO) 3 Mo•, •Mo(CO) 3 Cp′] radical cage pair, F c ′ was found to be smaller than F cP in solutions having the same viscosity. It is proposed that the difference in F cP and F c ′ arises because the radicals in the collisional cage pair are less likely to have the correct orbital orientation for radical−radical combination to occur, whereas photochemically generated geminate cage pairs are more likely to have the correct orbital orientation. As predicted, F cP and F c ′ both increase when the microviscosity of a solution increases.

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Section: Resultsmentioning

confidence: 99%

Solvent Cage Effects: A Comparison of Geminate and Nongeminate Radical Cage Pair Combination Efficiencies

Barry

Tyler

2020

Inorg. Chem.

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“…The new peaks, a1-c, may be assigned to the expected products of reaction 11 and 12, in accord with comparable reactions in the literature. 21 These products indicate that little propan-2-ol is generated in crossreactions; i.e., they lead to a negligible contribution to its polarization.…”

Section: Results and Analysismentioning

confidence: 99%

Radical Addition Rates to Alkenes by Time-Resolved CIDNP: 2-Hydroxy-2-propyl Radicals

Batchelor

Fischer

1996

J. Phys. Chem.

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A novel time-resolved CIDNP technique is used to measure absolute rate constants for the addition of 2-hydroxy-2-propyl radicals to 10 1,1-and two 1,2-disubstituted alkenes in propan-2-ol-d 8 and toluene-d 8 solvents and in part in acetonitrile-d 3 and cyclohexane-d 12 , at room temperature. 2-Hydroxy-2-propyl radicals are produced by photolysis of 2,4-dihydroxy-2,4-dimethylpentan-3-one and lead to a multiplet effect CIDNP of the self-termination product, propan-2-ol, which follows a second-order termination kinetics. Addition of alkene partially quenches this polarization through the addition reaction. Quantitative measurement of the time-dependence and its simulation by kinetic equations yields the addition rate constant k a . The technique is applicable to systems with rate constants between 10 5 and 10 9 M -1 s -1 , a range covered by the alkenes used. The data correlate with the alkene electron affinity and confirm the 2-hydroxy-2-propyl radical as very nucleophilic. A solvent dependence of k a up to 1 order magnitude is observed and is related to the hydrogenbonding ability of the solvent and radical and to the polarity of the solvent. A -steric effect of the alkene substituents is also noted.

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“…We obtained no evidence for the formation and trapping of > C e N radicals in the >C=C=N' form (33)(34)(35). A similar failure to trap 1-cyano radicals in the keten.kine form has been noted before (15,26) and is perhaps not surprising as spin traps have not been routinely successful at trapping nitrogen-centered radicals (4).…”

Section: Azo-compound Thermal Decomposition Studiesmentioning

confidence: 58%

Electron paramagnetic resonance study of the reactions of the spin trap 2,4,6-tribromonitrosobenzene in benzene solutions

Smith¹,

Maples²,

Lau³

1992

Can. J. Chem.

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PETER SMITH, KIRK RANDALL MAPLES, and RAMONA LILLIAN LAU. Can. J. Chem. 70, 1 16 (1 992). By means of static-sample studies involving the thermal decomposition of symmetric azo compounds and the oxidation of substrates with nickel peroxide, we have characterized by electron paramagnetic resonance 12 spin adducts of 2,4,6-tribromonitrosobenzene, 1, in benzene at 25°C. In addition, we have used electron paramagnetic resonance spectroscopy to investigate benzene solutions of 1 both by itself and in the presence of olefins, and both in the presence and absence of light. Although 1 by itself did not give evidence for any free radical formation, when 1 was mixed with any one of the 11 olefins tested we could detect nitroxide formation. The presence of light did not affect our results. These observations support the "ene" reaction mechanism of nitroxide formation.Key words: 2,4,6-tribromonitrosobenzene, spin trapping, nickel peroxide.PETER SMITH, KIRK RANDALL MAPLES et RAMONA LILLIAN LAU. Can. J. Chem. 70, 116 (1992). Faisant appel a des etudes de resonance paramagnktique Clectronique (rpe) sur des Cchantillons statiques impliquant la decomposition thermique des composes azo symetriques et l'oxydation de substrats avec le peroxyde de nickel, on a caractCrisC 12 adduits de spin du 2,4,6-tribromonitrobenzkne, 1, dans le benzkne, B 25°C. De plus, on a utilise la rpe pour Ctudier des solutions benzCniques du composC 1 soit seul ou en presence d'olefines, tant en prCsence qu'en absence de lumikre. M&me si le compose 1 seul ne semble pas donner naissance a la formation de radicaux libres, on a pu dktecter la presence de nitroxydes a chaque fois que le compose 1 a CtC mClangC avec l'une des 11 olefines Ctudiees. La presence de lumikre ne modifie pas nos resultats. Ces resultats sont en accord avec un mecanisme de rkaction cckne,, pour la formation du nitroxyde.Mots cle's : 2,4,6-tribromonitrobenzkne, piegeage de radicaux, peroxyde de nickel.[Traduit par la redaction]

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The Mechanism of Decomposition of Azo Compounds. II. Cage Effects in the Decomposition of α,α-Azoisobutyronitrile and Related Compounds

Cited by 84 publications

References 3 publications

Solvent Cage Effects: A Comparison of Geminate and Nongeminate Radical Cage Pair Combination Efficiencies

Solvent Cage Effects: A Comparison of Geminate and Nongeminate Radical Cage Pair Combination Efficiencies

Radical Addition Rates to Alkenes by Time-Resolved CIDNP: 2-Hydroxy-2-propyl Radicals

Electron paramagnetic resonance study of the reactions of the spin trap 2,4,6-tribromonitrosobenzene in benzene solutions

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