Free Radicals by Mass Spectrometry: Vii. The Ionization Potentials of Ethyl, Isopropyl, and Propargyl Radicals and the Appearance Potentials of the Radical Ions in Some Derivatives

Farmer, J. B.; Lossing, F. P.

doi:10.1139/v55-104

Cited by 67 publications

(16 citation statements)

References 14 publications

(13 reference statements)

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“…The free radicals were produced by the thermal decomposition of suitable derivatives in a fused-silica capillary furnace leading directly to the ionization chamber of a mass spectrometer. 11 The method of comparison of the ionization efficiency curves for the parent radical ion with that of an added standard gas was the same as employed formerly.18…”

Section: Methodsmentioning

confidence: 99%

The Photolysis of Carbon Suboxide. II. Effect of Added Oxygen

Bayes¹

1963

J. Am. Chem. Soc.

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Section: Methodsmentioning

confidence: 99%

The Photolysis of Carbon Suboxide. II. Effect of Added Oxygen

Bayes¹

1963

J. Am. Chem. Soc.

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“…The relative energies of the HOMOs of the allyl and 1-methylallyl fragments is afforded through comparison of the ionization potentials (20) of methylamine (8.97 eV) and dimethylamine (8.24 eV) , as well as of methyl (9.95 eV) and ethyl (8.78 eV) radicals (21,22). Thus the introduction of a methyl group is associated with a decrease in ionization potential, which indicates that the energy of the HOMO for the 1-methylallyl fragment in our system is higher than that for the unsubstituted allyl fragment, in both the reactant and the intermediate.…”

Section: Effect Of Methyl Substitutionmentioning

confidence: 99%

Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution

Buncel¹,

Joly²,

Jones³

1986

Can. J. Chem.

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. Can. J. Chem. 64, 1240Chem. 64, (1986. The rate-pH profile for detritiation from the C-2 position of 1-methylimidazole has been determined in aqueous solution at 85°C. The profile is consistent with a mechanism involving attack by hydroxide ion on the conjugate acid of the substrate to give an ylid intermediate in the rate-determining step. At higher pH, hydroxide-catalyzed exchange of the neutral species becomes increasingly important. Comparison of the second-order rate constants derived from the rate-pH profiles of imidazole, 1-methylimidazole, benzimidazole, and 1-methylbenzimidazole showed that methyl substitution caused the rate to increase by 2-to 3-fold while benzo annelation increased the rate by 10-to 20-fold. Frontier molecular orbital (FMO) analysis of the reaction scheme for proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives has been used to explain the rate-accelerating effect of methyl substitution and benzo annelation in these processes.ERWIN BUNCEL, HELEN A. JOLY et JOHN R. JONES. Can. J. Chem. 64, 1240Chem. 64, (1986.Opkrant a 85°C et dans une solution aqueuse, on a determink un profil de la vitesse/pH pour la rkaction de dCtritiation de la position C-2 du mkthyl-1 imidazole. Le profil est en accord avec un mecanisme impliquant une ttape dkterminante dans laquelle un ion hydroxyde attaque l'acide conjuguk du substrat pour conduire a un ylide intermediaire. A des pH plus ClevCs, 1'6change catalysC par des bases des espkces neutres devient de plus en plus important. Une cornparaison des constantes de vitesse du deuxikme ordre, obtenues ? I partir des profils de vitesse/pH, des imidazole, mkthyl-1 imidazole, benzimidazole et mCthyl-1 benzimidazole a perrnis de montrer que la substitution par des groupements mkthyles multiplie la vitesse par 2 h 3 alors que l'annelation par un noyau benzknique multiplie les vitesses par 10 a 20. Dans le but d'expliquer I'acckltration de la vitesse lors de substitutions par des groupements mtthyles et lors de l'annelation par des cycles benzkniques, on a utilisk une analyse, par les orbitales molkculaires frontihres, du schkma rkactionnel des transferts protoniques de l'imidazole, du benzimidazole et de leurs derives substitues par un groupement rnethyle en position 1.[Traduit par la revue]The rate of hydrogen isotope exchange from the C-2 position of the imidazole ring is of interest, in part because of its presence in biologically important systems such as adenine and guanine, fundamental components of nucleic acids, and in drugs such as purornycin. Imidazole is also the primary component of histidine which is present at the active site of many enzymes. The importance of the imidazole ring can be coupled with the use of deuterium and tritium labels as probes in the investigation of chemical and biochemical processes. For instance, the rate of hydrogen isotope exchange from the C-2 position of the imidazole nucleus present in the histidine residues of the enzymes p-lactamase I1 and superoxide dismutase has been used to identify the s...

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“…However, the retention of configuration following the He3H+ attack rules out the intermediacy of linear pentyl ions and provides the first unambiguous evidence for the occurrence of the gaseous protonated cyclopropanes, often postulated on energetic grounds, or from the fragmentation pattern of isotopically labeled molecules, in a number of mass spectrometric investigations. [48][49][50][51][52][53][54][55][56] C. The Fragmentation Products. The excited cyclopropanium ions that escape collisional stabilization undergo fragmentation processes leading to labeled products other than cyclopropanes.…”

Section: Discussionmentioning

confidence: 99%

Reactions of helium tritide ions with gaseous hydrocarbons. V. cis- and trans-1,2-Dimethylcyclopropane. Unambiguous evidence for gaseous protonated cyclopropanes

Cacace¹,

Guarino²,

Speranza³

1971

J. Am. Chem. Soc.

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In order to gather direct chemical evidence for the occurrence of protonated cyclopropanes as intermediates in a gas-phase reaction, gaseous cis-and trans-l ,2-dimethylcyclopropane were allowed to react with a gaseous Brpnsted acid, the helium tritide ion formed from the ß decay of molecular tritium. The cis and trans isomers gave the corresponding tritiated compounds retaining the configuration of the original molecules. The lack of any measurable cis-trans isomerization lends strong support to the view that the formation of the tritiated cycloalkanes, following the transfer of a triton from He1 23H+ to the substrate, proceeds via a cyclic intermediate, and does not involve the cleavage of the cyclopropane ring. These results corroborate the mechanistic interpretation of earlier experiments concerning the triton transfer from He3H+ to unsubstituted cycloalkanes, and provide unambiguous evidence for the intermediacy of protonated cyclopropanes in a gas-phase reaction.In recent years, we focused our attention on the use

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Free Radicals by Mass Spectrometry: Vii. The Ionization Potentials of Ethyl, Isopropyl, and Propargyl Radicals and the Appearance Potentials of the Radical Ions in Some Derivatives

Cited by 67 publications

References 14 publications

The Photolysis of Carbon Suboxide. II. Effect of Added Oxygen

The Photolysis of Carbon Suboxide. II. Effect of Added Oxygen

Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution

Reactions of helium tritide ions with gaseous hydrocarbons. V. cis- and trans-1,2-Dimethylcyclopropane. Unambiguous evidence for gaseous protonated cyclopropanes

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