Triplet Methylene Research Articles

CHLORIDE ENHANCEMENT OF QUENCHING OF TRIPLET METHYLENE BLUE BY Fe(II)

Abstract— The influence of chloride ion on the rate of decay of triplet methylene blue in 0.01 M acid in the absence and presence of ferrous ions was investigated by means of laser flash‐photolysis monitored by kinetic spectrophotometry. Chloride weakly accelerates decay of 3MBH2± in aqueous solution in the absence of Fe(II). Quenching of 3MBH2+ by Fe(II) is more strongly catalyzed by Cl‐ in both water and 50 v/v% aq. CH3CN. The uncatalyzed quenching constant, k5, is of the order of 1 × 106M‐1 s‐1 while in 4.8 M aqueous chloride (μ– 7.2 M) k5= (37.2 ± 1.8) × 106M‐1 s‐1. A possible role of chloride is as a bridging species in quenching via electron transfer between 3MBH2+ and Fe(II).

Electron Transfer Reactions between Triplet Methylene Blue and Ferrocenes in Acetonitrile

Electron Transfer Reactions between Triplet Methylene Blue and Ferrocenes in Acetonitrile

Keten photochemistry. Some observations on the reactions and reactivity of triplet methylene

Molecular hydrogen, observed in three different kinds of experiment, is argued to be a product of triplet methylene recombination; the addition reaction of triplet methylene with acetylene is slower than previously thought.

A partial open shell FSGO calculation on the triplet methylene abstraction reaction with the hydrogen molecule: 3CH 2 + H 2 = CH 3 + H

A partial open shell FSGO method is used to study the reaction path for the triplet methylene abstraction reaction with the hydrogen molecule, and the results obtained compare favourably with those from larger ab initio calculations.

Calculated photoelectron spectra of singlet and triplet methylene

Vertical ionization potentials for singlet and triplet methylene are calculated by a CI perturbation method based on ab initio SCF molecular orbitals (6–31 G** basis). The shape and vibrational fine structure of the first photoelectron band are investigated using the MINDO/3 method. The computed singlet-triplet splitting for methylene is 16.4 kcal/mol, in reasonable agreement with the experimental value of 19.5 kcal/mol.

Reactions of carbynes. Potential energy surfaces for the doublet and quartet methylidyne (CH) reactions with molecular hydrogen

The CH(2Π)+H2→CH3 and CH(4Σ−)+H2→CH2(3B1)+H reactions have been studied using ab initio molecular electronic structure theory. Basis sets used were of double zeta (DZ) quality and DZ augmented by polarization functions. For the insertion reaction, the least motion barrier height is quite high, ∼75 kcal/mole. However, nonleast motion pathways are much more favorable, involving little or no barrier. In both respects this potential energy surface is analogous to that for the methylene insertion CH2(1A1)+H2→CH4. The quartet abstraction has a sizeable barrier, ∼11 kcal, associated with it, in analogy with the triplet methylene abstraction CH2(3B1)+H2→CH3+H.

ChemInform Abstract: FLASH PHOTOLYSIS OF KETENE. PHOTOLYSIS MECHANISM AND RATE CONSTANTS FOR SINGLET AND TRIPLET METHYLENE

Chemischer InformationsdienstVolume 8, Issue 28 Preparative Organic Chemistry ChemInform Abstract: FLASH PHOTOLYSIS OF KETENE. PHOTOLYSIS MECHANISM AND RATE CONSTANTS FOR SINGLET AND TRIPLET METHYLENE M. J. PILLING, M. J. PILLINGSearch for more papers by this authorJ. A. ROBERTSON, J. A. ROBERTSONSearch for more papers by this author M. J. PILLING, M. J. PILLINGSearch for more papers by this authorJ. A. ROBERTSON, J. A. ROBERTSONSearch for more papers by this author First published: July 12, 1977 https://doi.org/10.1002/chin.197728111AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue28July 12, 1977 RelatedInformation

Rates of spin-forbidden organic reactions. Theoretical study of the rate of direct production of triplet methylene by dissociation of singlet diazomethane

Rates of spin-forbidden organic reactions. Theoretical study of the rate of direct production of triplet methylene by dissociation of singlet diazomethane

Reaction between triplet methylene and CO2: rate constant determination

The rate constant (k3) for the reaction 3CH2 + CO2 → HCHO + CO has been measured using flash photolysis in conjunction with both gas chromatography and kinetic spectroscopy. k3 was found to be (3.9 ± 1.9) × 10−14 cm3 molecule−1 s−1. CO, vibrationally excited to at least ν′ = 2 is a product of the reaction. The rate constant for the abstraction by triplet CH2 from CH2N2 to produce CH3 was determined to be 1.0 × 10−12 cm3 molecule−1 s−1.

Kinetics of methylene addition to cis- and trans-but-2-ene. Further evidence for the energy separation between triplet and singlet methylene

The reactions of triplet and singlet methylene with cis- and trans-but-2-ene have been studied over the temperature range 350–473 K. The results yield a value of (36.5 ± 3.2) kJ mol–1 for the energy separation between singlet and triplet methylene, and provide further confirmation of the assumption that singlet methylene reactions with hydrocarbons proceed with activation energies close to zero. Previous evidence for the similar reactivities of triplet methylene and the methyl radical receives additional support.

Flash photolysis of ketene. Photolysis mechanism and rate constants for singlet and triplet methylene

The photochemistry of ketene has been studied, using flash photolysis coupled with end product analysis, for wavelengths above 160 nm. The data were analysed numerically, enabling the proposed reaction mechanisms to be assessed quantitatively. The major novel feature is the observation of products normally derived from CH21A1 at high pressures where deactivation to CH23B1 is expected to be complete. It is suggested that these products derive from CH21B1 is expected to be complete. It is suggested that these products derive from CH21B1. The data require that this state is comparatively stable with respect to collisional deactivation, but reacts with H2(k= 2 × 10–11 cm3 molecule–1 s–1) and CH2CO (k= 3 × 10–11 cm3 molecule–1 s–1). These rate constants depend on an assumed radiative lifetime (1/e) for CH21B1 of 10–6 s. An anomalously high yield of acetylene is found at low pressures in the presence of hydrogen. Rate constants for CH21A1 with CH2CO and CH23B1 with C2H2, NO, O2 and CO are reported.

The Electron Transfer Reaction between Triplet Methylene Blue and Aromatic Compounds

The Electron Transfer Reaction between Triplet Methylene Blue and Aromatic Compounds

ANION AND SOLVENT EFFECTS ON THE RATE OF REDUCTION OF TRIPLET EXCITED THIAZINE DYES BY FERROUS IONS

Abstract— The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl‐sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.

THE PHOTOREDUCTION OF METHYLENE BLUE BY AMINES—I. A FLASH PHOTOLYSIS STUDY OF THE REACTION BETWEEN TRIPLET METHYLENE BLUE AND AMINES

Abstract— Flash photolysis was used to study the reduction of the triplet state of methylene blue by both alkyl‐ and aryl‐amines. The extent of the formation of the semireduced form of the dye yielded rate constants of interaction between the triplet state and the amine (k5). A correlation between log k5 and ionization potentials for alkylamines (slope = ‐1.75 eV‐1) was interpreted as evidence for the formation of a partial charge‐transfer intermediate. The rate constants (k5) calculated for aryl‐amines approached the rate of diffusion in many cases. A Hammett plot for a series of N, N‐dimethyl‐anilines yielded a moderately large p value (– 3.28) consistent with the formation of a charge‐transfer intermediate. It was concluded that reaction of amines with triplet methylene blue leads to the formation of a partial charge‐transfer intermediate which may undergo complete electron transfer to yield radicals, or undergo spin inversion and return to the ground state.

Localized Molecular Orbital Studies of Chemical Reaction. II. Abstraction and Addition Reactions of Triplet Methylene

Abstract Energy-localized molecular orbitals (LMO) generated from UHF–INDO wave functions have been used for the studies of the mechanistic details of the abstraction and addition reactions of triplet methylene. The UHF LMO mapping procedure which we have previously developed permits a clear understanding of the nature of the chemical bonds to be formed or broken on reaction. Significance of the three-stage mechanism, which should involve the successive β- and α-spin electron delocalizations between reactants and the concomitant spin polarization of the reacting bond, is emphasized. The whole aspects of the reactions are well in accord with the customarily accepted mechanistic schemes.

Transition states for the abstraction reactions of triplet methylene with hydrogen and methane

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTransition states for the abstraction reactions of triplet methylene with hydrogen and methaneCharles W. Bauschlicher Jr., Charles F. Bender, and Henry F. Schaefer IIICite this: J. Am. Chem. Soc. 1976, 98, 11, 3072–3074Publication Date (Print):May 1, 1976Publication History Published online1 May 2002Published inissue 1 May 1976https://doi.org/10.1021/ja00427a002RIGHTS & PERMISSIONSArticle Views87Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (335 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: MECHANISM AND RATE CONSTANT OF THE REACTION BETWEEN METHYLENE AND METHYL RADICALS

The chemistry of the reaction between methyl and triplet methylene radicals has been examined by means of flash photolysis of azomethane and ketene followed by gas chromatographic analysis of the hydrocarbon products. Using the combination rate constant of triplet CH2 and the combination of CH3 a value for the reaction 3CH2 + CH3 to C2H5* to C2H4 + H has been determined.

Mechanism and rate constant of the reaction between methylene and methyl radicals

The chemistry of the reaction between methyl and triplet methylene radicals has been examined by means of flash photolysis of azomethane and ketene followed by gas chromatographic analysis of the hydrocarbon products. Using the combination rate constant of triplet CH2 and the combination of CH3 a value for the reaction 3CH2 + CH3 to C2H5* to C2H4 + H has been determined.

A rate constant for CH 2( 3B 1) + CH 3

Triplet methylene, CH 2( 3B 1), and methyl radicals were produced by flash photolysis of a mixture of ketene and azomethane. A computer fit of the product ratios, using the known rate constants for CH 2 + CH 2, and CH 3 + CH 3, requires a rate constant of 5.0 × 10 −11 cm 3 molecule −1s −1 for the reaction CH 2 + CH 3 − C 2H 4 + H.

Further kinetic evidence for the energy separation between triplet and singlet methylene

An investigation of the reactions of methylene with cis-but-2-ene, in excess of nitrogen, as a function of temperature yielded results which are interpreted in terms of a high (ca. 38 kJ mol–1) energy separation between triplet and singlet methylene.