NN′-dimethylporphyrins

Dearden, G. R.; Jackson, Anthony H.

doi:10.1039/c29700000205

Cited by 20 publications

(11 citation statements)

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“…45 The main argument against this mechanism, with respect to the selective formation of 2-chlorooctane, is that it would in all likelihood be restricted to cases in which an octane molecule is situated next to an heptane molecule that is being ionized directly by the radiation and subsequently dissociates and, as a consequence, G'values for this process would be expected to remain constant with octane concentration, whereas experimentally the G'value of 2-chlorooctane is observed to decrease quite drastically with the concentration of octane (see Figure 5). Unlike positivehole migration, long-range migration of the positive charge by hydride transfer from heptanemolecules to heptane radical cations does not appear to be a likely process.…”

Section: Esr Evidence For Proton Transfer From Heptane Radicalmentioning

confidence: 97%

Site Selectivity in the Proton Transfer from Alkane Radical Cations to Alkane Molecules. Donor and Acceptor Site Selectivity in the Proton Transfer from Heptane Radical Cations to Octane Molecules in .gamma.-Irradiated n-C7H16/n-C8D18 and n-C7H16/n-C8H18/1-C6H13Cl Crystals at 77 K

Demeyer¹,

Stienlet²,

Ceulemans³

1994

J. Phys. Chem.

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Heptyl radicals formed by y-irradiation of n-C7Hl6, both in neat form and with various concentrations of n-CsDls added before irradiation, are investigated by ESR spectroscopy. It is observed that the presence of deuterated octane in protiated heptane results in a substantial increase in the relative contribution of protiated 1 -heptyl radicals to the radical spectrum. Their formation is attributed to the proton-transfer reaction (n-C7H16*+ + n-CsDl8 -1-C7H15* + n-CsDlgH+) which, in accordance with an earlier and experimentally verified postulate stating that a strict relation exists between the radical site in alkyl radicals formed by proton transfer from alkane radical cations to alkane molecules and the structure of the semioccupied molecular orbital of the parent cation, is expected to yield l-heptyl radicals selectively. The increase in the relative importance of l-heptyl vs other isomeric heptyl radicals as a result of the presence of octane in heptane is confirmed by analysis of the tetradecanes formed by irradiation of heptane/ l-chlorohexane( 1 mol %) and heptane/lchlorohexane( 1 mol%)/octane(9 mol 7%) systems. As to the acceptor site, a study is made by gas chromatography of the yield and isomeric composition of chlorooctanes formed by y-irradiation of n-C.1Hl6, containing 1 mol 5 % l-C6H1&1 and various concentrations of n-CsHls. Formation of chlorooctanes in such systems is largely due to neutralization of protonated octane molecules by chloride ions (CsH19+ + C1--CsH17Cl+ H2). The isomeric composition yields direct information on the proton-acceptor site in the octane molecule. It is observed that mainly 2-chlorooctane is formed, with much smaller yields of 1-and 3-chlorooctane; the formation of 4-chlorooctane is still less pronounced. The selective formation of 2-chlorooctane, which can be rationalized on the basis of structural considerations and of the fact that the proton affinity for primary C-H protonation is smaller than for secondary C-H protonation, confirms that proton transfer to octane molecules takes place from the chain-end position in extended heptane radical cations and indicates that octane solute molecules are packed quite regularly and with conservation of the layer structure in the heptane crystal. Various alternative mechanisms for chlorooctane formation are discussed and are are discarded with respect to the selective formation of 2-chlorooctane on various grounds. The results obtained further support the postulate stating that a strict relation exists between the proton-donor site in the proton transfer from alkane radical cations to alkane molecules and the structure of the semi-occupied molecular orbital of the parent cation.

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Section: Esr Evidence For Proton Transfer From Heptane Radicalmentioning

confidence: 97%

Site Selectivity in the Proton Transfer from Alkane Radical Cations to Alkane Molecules. Donor and Acceptor Site Selectivity in the Proton Transfer from Heptane Radical Cations to Octane Molecules in .gamma.-Irradiated n-C7H16/n-C8D18 and n-C7H16/n-C8H18/1-C6H13Cl Crystals at 77 K

Demeyer¹,

Stienlet²,

Ceulemans³

1994

J. Phys. Chem.

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“…Tais adutos são selecionados por massa e o analito quiral é substituído em uma reação com um gás neutro (quiral ou aquiral). A distinção quiral é possível porque a velocidade de troca varia com a quiralidade do analito incorporado dentro do hospedeiro quiral 23,[27][28][29] ; (c) a terceira metodologia é baseada na dissociação induzida por colisão (CID) de adutos diasteroisoméricos formados pelo analito e uma referência quiral em um experimento de espectrometria de massas sequencial (MS/MS) 30-35 e, (d) o assunto explorado neste trabalho, usa também a espectrometria de massas sequencial, mas emprega o método cinético para quantificação dos efeitos quirais 36,37 .…”

Section: Resolução Quiral Por Espectrometria De Massasunclassified

Análise quiral por espectrometria de massas através da utilização do método cinético

Augusti¹,

Augusti²

2006

Quím. Nova

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Recebido em 17/12/04; aceito em 21/7/05; publicado na web em 20/1/06 CHIRAL ANALYSIS BY MASS SPECTROMETRY USING THE KINETIC METHOD. Novel and quantitative mass spectrometry methods for rapid and accurate enantiomeric excess determination are presented. These methodologies use electrospray ionization (ESI) and mass spectrometry (MS) to detect and analyze, via collision-induced dissociation (CID), mass-selected transition metal complexes that promote enantio especific interactions. The data from CID are conveniently treated by the kinetic method, a sensitive linear free energy method of treating mass spectrometric results. Four different variations of this methodology are described: single ratio method (S R ), quotient ratio method (Q R ), fixed ligand method (S R fixed ), and quotient ratio method with fixed ligand (Q R fixed ). These individual methods are compared and their main features discussed in detail.

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“…A large number of biological and pharmaceutical reactions involve the abstraction of hydrogen, often as a primary step in the reaction sequence. An established method of examining hydrogen abstraction reactions is by use of a hydrogen-deficient, stable free radical, such as %,a-diphenyl-/?-picrylhydrazyl (DPPH) (Dearden, 1971). However, the characteristics that bestow stability on a free radical generally tend also to bestow water-insolubility; whilst certain of the nitroxides are reasonably soluble in water, they are poor hydrogen abstractors.…”

Section: School Of Pharmacy Liverpool Polytechnic Byrom Street LIVmentioning

confidence: 99%

A stable free radical for the investigation of hydrogen abstraction reactions in aqueous solution

Dearden

Odusina

1971

Journal of Pharmacy and Pharmacology

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NN′-dimethylporphyrins

Abstract: The formation and some spectroscopic properties of NN'-dimethylaetioporphyrin-I and NN'-dimethyloctaethylporphyrin are described.

Cited by 20 publications

References 0 publications

Site Selectivity in the Proton Transfer from Alkane Radical Cations to Alkane Molecules. Donor and Acceptor Site Selectivity in the Proton Transfer from Heptane Radical Cations to Octane Molecules in .gamma.-Irradiated n-C7H16/n-C8D18 and n-C7H16/n-C8H18/1-C6H13Cl Crystals at 77 K

Site Selectivity in the Proton Transfer from Alkane Radical Cations to Alkane Molecules. Donor and Acceptor Site Selectivity in the Proton Transfer from Heptane Radical Cations to Octane Molecules in .gamma.-Irradiated n-C7H16/n-C8D18 and n-C7H16/n-C8H18/1-C6H13Cl Crystals at 77 K

Análise quiral por espectrometria de massas através da utilização do método cinético

A stable free radical for the investigation of hydrogen abstraction reactions in aqueous solution

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