Methanol Radical Research Articles

Density functional theory studies of the methanol radical cation hypersurface

A variety of density functional theory (DFT) methods and basis sets have been used to study the equilibrium of the formaldehyde and trans-hydroxymethylene radical cations. The Becke3LYP/6-311 + G ∗∗ method is the best compromise between accuracy and computational effort of the methods tested. This method has been used for a comprehensive study of the fragmentation and isomerization reactions of the cations, radicals and radical cations derived from the methanol radical cation. The energies and geometries obtained are compared to those of a G2 study previously reported by Ma et al. (J. Am. Chem. Soc., 113 (1991) 7903) and to the available experimental data to evaluate the performance of this DFT method for radical ions. The relative energies of the minima and transition structures studied are in good agreement with the experimental data. The trends and relative stabilities obtained by the Becke3LYP/6-311 + G ∗∗ calculations are very similar to the results from the G2 method, even though the values for the relative energies are systematically higher. With the exception of ion-molecule complexes, the geometries obtained are also very close to those obtained by the G2 method.

Refined thermochemistry for the methanol radical cation (CH3OH.cntdot.+) and its distonic isomer (CH2OH2.cntdot.+)

Ab initio molecular orbital calculations at levels of theory beyond G2 have been used to obtain the ionization energy (IE a ) of methanol and the energy difference (ΔE 298 ) between CH 3 OH .+ and the methyleneoxonium radical cation, CH 2 OH 2 .+ . The best estimate of IE a is 1051 kJ mol -1 , compared with the experimental value of 1047 kJ mol -1

Rearrangement and dissociative reactions of the methanol radical cation (CH3OH.bul.+): a comparison of theory and experiment

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRearrangement and dissociative reactions of the methanol radical cation (CH3OH.bul.+): a comparison of theory and experimentNgai Ling Ma, Brian J. Smith, John A. Pople, and Leo RadomCite this: J. Am. Chem. Soc. 1991, 113, 21, 7903–7912Publication Date (Print):October 1, 1991Publication History Published online1 May 2002Published inissue 1 October 1991https://doi.org/10.1021/ja00021a013RIGHTS & PERMISSIONSArticle Views191Altmetric-Citations65LEARN 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 (1018 KB) Get e-Alerts Get e-Alerts

The reactivity of various free radicals with hyaluronic acid: steady-state and pulse radiolysis studies

The reactions of the primary water radicals with the biopolymer hyaluronic acid have been studied by pulse radiolysis. Bimolecular rate constants, expressed in terms of the disaccharide repeating sub-unit of hyaluronic acid, for OH ., H . and e aq − were found to be 7 ṡ 10 8 M −1 ṡ s −1, 5 ṡ 10 7 M −1 ṡ s −1 and <5 ṡ 10 6 M −1 ṡ s −1, respectively. By comparing the viscosities of samples, γ-irradiated in the steady state under a variety of conditions, with unirradiated controls, the efficiencies with which selected radicals cause chain breakage have been determined. Efficiencies of 30%, 15%, 0%, 0.2% and 5% were estimated for OH ., H ., e aq −, methanol radicals and tert-butanol radicals, respectively. The presence of oxygen during irradiation increased the extent of chain breakage by a factor of 1.75.

Reaction of alcohol radicals with cyclic disulfides. An optical and conductimetric pulse radiolysis study

The disulfides lipoamide (LIPA) and oxidized dithiothreitol ( ox-DTT) react with methanol, ethanol, isopropanol and t-butanol radicals in aqueous solution at pH10.8 to form disulfide radical anions. Electron transfer rates range from ca 10 7 dm 3 mol -1s -1 for t-butanol radicals with LIPA to 3.6 × 10 8 dm 3 mol -1s -1 for methanol radicals with LIPA. The formations of the disulfide radical anions were followed by simultaneously monitoring absorption changes at 400 nm and changes in conductance with time. The electron transfer efficiencies are higher for LIPA than for ox-DTT increasing in the series t-butanol ⪡isopropanol 〈ethanol ∼methanol and are less than the proportion of α-carbon radical formation on the alcohols.

Further pulse radiolysis studies of decacarbonyldimanganese(O) and decacarbonyldirhenium(O). Temperature and solvent effects

Pulse radiolysis of Mn 2(CO) 10 and Re 2(CO) 10 in alcohol and isooctane solutions over the temperature ranges −43 to 22 °C (for Mn 2(CO) 10) and 22 to 106 °C (for Re 2(CO) 10) has been investigated. At room temperature, Mn 2(CO) 10 affords the Mn(CO) 5• radical in both ethanol and methanol. However, at −27 (in ethanol) and −37 °C (in methanol), a transient is generated that exhibits an absorption band with a maximum at 700 nm and a molar extinction coefficient, in ethanol, of ϵ 700 10,120 ± 150 M −1 cm −1. This species decays by first-order kinetics with a rate constant of k = 1.1 × 10 5 s −1, and has been tentatively formulated as a product of protonation of Mn 2(CO) 10 ⨪ by the solvent. Pulse irradiation of Re 2(CO) 10 in ethanol solution up to 60 °C, and in 1-butanol solution up to 106 °C, produces what appears to be the corresponding protonated dirhenium species, but no detectable Re(CO) 5• radical. By way of contrast, both Mn 2(CO) 10 and Re 2(CO) 10 yield their respective pentacarbonyl radicals on pulse irradiation in isooctane solution. The values of E a for the reactions of Mn(CO) 5• and Re(CO) 5• with CCl 4 and for the coupling reaction of Mn(CO) 5•, all in ethanol solution, were found to be 2.8, 2.5, and 2.1 kcal/mol, respectively.

The structure and dissociation pathways of protonated methanol: An ab initio molecular orbital study

AbstractAb initio molecular orbital calculations with moderately large polarization basis sets and including valence‐electron correlation have been used to examine the structure and dissociation mechanisms of protonated methanol [CH3OH2]+. Stable isomers and transition structures have been characterized using gradient techniques. Protonated methanol is found to be the only stable isomer in the [CH5O]+ potential surface. There is no evidence for a tightly‐bound complex, [HOCH2]+…︁H2, analogous to the preferred structure [CH3]+…︁H2 of [CH5]+. Protonated methanol is found to possess a pyramidal arrangement of bonds at the oxygen atom with a barrier to inversion of 8kJ mol−1. The lowest energy fragmentation pathways are dissociation into methyl cation and water (predicted to require 284 kJ mol−1 with zero reverse activation energy) and loss of molecular hydrogen (endothermic by 138 kJ mol−1 but with a reverse activation barrier of 149 kJ mol−1). The results offer a possible explanation as to why production of [CH2OH]+ from the reaction of methyl cation with water is not observed. Other dissociation processes examined include loss of a hydrogen atom to yield the methylenoxonium radical cation or methanol radical cation (requiring 441 and 490 kJ mol−1, respectively) and loss of a proton to yield neutral methanol (requiring 784 kJ mol−1).

ChemInform Abstract: AN ESR STUDY OF ELECTRON REACTIONS WITH CARBOXYLIC ACIDS, KETONES, AND ALDEHYDES IN AQUEOUS GLASSES

AbstractDie auf 77 Kgekühlte Lösung von 12 M LiCl, l0 mM K4[Fe‐ (CN)6] und O.l‐0.5 M Carbonsäure, Keton oder Aldehyd wird mit 2537 Å photolysiert ( 1 min).

Transient phenomena in the pulse radiolysis of retinyl polyenes. 1. Radical anions

The spectra and kinetics of formation and decay of radical anions of a number of retinyl polenes have been studied in methanol and 2-propanol at room temperature, using pulse radiolysis and kinetic spectrophotometry. The bimolecular rate constants for the attachment of solvated electrons, e/sup -//sub MeOH/, to the retinyl polyenes are in the diffusion-controlled limit (8.6 x 10/sup 9/-1.6 x 10/sup 10/ M/sup -1/ s/sup -1/). The radical anions of retinol and retinol acetate have their spectral maxima at 370 to 390 nm, and undergo decay very slowly with second-order kinetics. On the other hand, the radical anions of retinal, retinal n-butylamine Schiff base, and retinoic acid/ester have spectral maxima at 430 to 510 nm, and decay by first-order kinetics in methanol with rate constants in the range 1 x 10/sup 4/ - 1 x 10/sup 6/ s/sup -1/. The decay rates of radical anions of retinal and retinoic acid/ester become considerably longer on going from methanol to less acidic alcohol, 2-propanol, suggesting that protonation by sovent is the major mode of their decay in protic media. In the case of retinal Schiff base, an additional slow process with bimolecular rate constant 9.0 x 10/sup 7/ M/sup -1/ s/sup -1/more » in methanol is observed for the formation of radical anion and is ascribed to the electron-transfer reaction from the methanol radical, CH/sub 2/OH. 6 figures.« less

An ESR study of electron reactions with carboxylic acids, ketones, and aldehydes in aqueous glasses

Electron reactions with a number of carboxylic acids, ketones, and aldehydes were investigated in a deuterated neutral aqueous glass at 77 K by ESR spectroscopy. Free radical reactions which took place upon warming the glasses to temperatures at which the electron adducts become mobile were studied. For carboxylic acids (C/sub n/H/sub 2n+1/CO/sub 2/D, n = 2,3) the deuterated anion radicals (RCH/sub 2/C(OD)/sub 2/) give results which suggest abstraction of a hydrogen from the parent acid to produce radicals of structure RCHCO/sub 2/D. The formic acid deuterated anion is found to undergo a similar mechanism. The acetic acid deuterated anion is not found to abstract from acetic acid, but is found to abstract from isopropyl alcohol. Ketone electron adducts are also found to abstract from their parent compounds to yield radicals of structure RCHC(O)R' with R and R' = CH/sub 3/, C/sub 2/H/sub 5/. Electron reactions with five aldehydes (RCHO with R = H, CH/sub 3/, C/sub 2/H/sub 5/, C/sub 3/H/sub 7/, and i-C/sub 3/H/sub 7/) gave their corresponding alcohol radicals (RCHOD) after deuteration at 77 K. Radicals with R = C/sub 2/H/sub 5/, C/sub 3/H/sub 7/, and i-C/sub 3/H/sub 7/ were found to abstract from the parent aldehyde to formmore » radicals of structure RR'CCHO. The methanol radical (CH/sub 2/OD) showed no further reaction while the ethanol radical (CH/sub 3/CHOD) resulted in the production of the diacetal anion. The results for acids, aldehydes, and ketones show that radicals of structure RC(OD)R' with R' = OD, H, or an alkyl group can act as hydrogen atom abstracting agents.« less

ChemInform Abstract: ELECTRON TRANSFER AND ADDITION REACTIONS OF FREE NITROXYL RADICALS WITH RADIATION INDUCED RADICALS

The mechanism of the reactions of free nitroxyl radicals [2,2,5,5-tetramethyl-1-pyrrolidinyl-oxy-3-carboxamide; 2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy-3-carboxamide; 4-hydroxy-2,2,6,6-tetramethyl-piperidino-1-oxy (TMPN); 2,2,6,6-tetramethyl-4-oxo-piperidino-oxy (TAN)] with radiation induced radicals has been investigated by pulse radiolysis conductivity measurements. The reaction [graphic omitted] proceeds by different simultaneous pathways. Electron transfer yields a [graphic omitted] ion which is stable over the acid and most of the basic pH range. At high pH it reacts according to [graphic omitted]. The OH radical also adds to the nitroxyl groups forming [graphic omitted] and to other activated sites of the nitroxyl radicals, e.g. to CC bonds. Reduction of [graphic omitted] and reducing α-hydroxy radicals yields [graphic omitted] in neutral and basic solutions. Radicals which are neither good oxidants nor reductants such as ·CH2CH2OH, ·CH2C(CH3)2OH, c-C5H9·, CH3· and CCl3·, generally add to the nitroxyl group to form [graphic omitted]. In acid solution all the adducts are protonated according to the equilibrium [graphic omitted]. The corresponding pK values are dependent on X and the nature of the nitroxyl compound. The methanol radical, ·CH2OH, forms an addition product [graphic omitted] which is either stabilized by protonation or decays unimolecularly (t½≈ 1 ms) to [graphic omitted] and HCHO. The rate constants for the reactions of [graphic omitted] with the radiation induced radicals are in the range 108–1010 dm3 mol–1 s–1.

ChemInform Abstract: TRIMERIC PRODUCTS FROM THE FREE RADICAL OXIDATION OF (Z)‐ISOEUGENOL

AbstractBei der Oxidation von Isoeugenol (II) mit dem Tri‐tert.‐butylphenoxyl‐Radikal [in situ aus dem Phenol (I)] werden vier trimere Oxidationsprodukte (IIIa), (IIIb), (IV) und (V) erhalten, deren Strukturen anhand eingehender Untersuchung der PMR‐ und Massenspektren geklärt werden.

Electron transfer and addition reactions of free nitroxyl radicals with radiation induced radicals

The mechanism of the reactions of free nitroxyl radicals [2,2,5,5-tetramethyl-1-pyrrolidinyl-oxy-3-carboxamide; 2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy-3-carboxamide; 4-hydroxy-2,2,6,6-tetramethyl-piperidino-1-oxy (TMPN); 2,2,6,6-tetramethyl-4-oxo-piperidino-oxy (TAN)] with radiation induced radicals has been investigated by pulse radiolysis conductivity measurements. The reaction [graphic omitted] proceeds by different simultaneous pathways. Electron transfer yields a [graphic omitted] ion which is stable over the acid and most of the basic pH range. At high pH it reacts according to [graphic omitted]. The OH radical also adds to the nitroxyl groups forming [graphic omitted] and to other activated sites of the nitroxyl radicals, e.g. to CC bonds. Reduction of [graphic omitted] and reducing α-hydroxy radicals yields [graphic omitted] in neutral and basic solutions. Radicals which are neither good oxidants nor reductants such as ·CH2CH2OH, ·CH2C(CH3)2OH, c-C5H9·, CH3· and CCl3·, generally add to the nitroxyl group to form [graphic omitted]. In acid solution all the adducts are protonated according to the equilibrium [graphic omitted]. The corresponding pK values are dependent on X and the nature of the nitroxyl compound. The methanol radical, ·CH2OH, forms an addition product [graphic omitted] which is either stabilized by protonation or decays unimolecularly (t½≈ 1 ms) to [graphic omitted] and HCHO. The rate constants for the reactions of [graphic omitted] with the radiation induced radicals are in the range 108–1010 dm3 mol–1 s–1.

A pulse radiolysis study of some platinum(II) and platinum(IV) complex ions in aqueous solutions. The formation and characterization of platinum(I) and platinum(III) transients

The technique of pulse radiolysis was used to study the reactions of the hydrated electron and H atom in aqueous media with platinum(II) amine complex ions: chloro-(diethylenetriamine) platinum(II), chloro(1,1,7,7-tetraethyldiethylenetriamine)platinum(II) and bis-(ethylenediamine) platinum(II). The second-order rate constants for these reactions are near 1 × 10 10 dm 3 mol −1 s −1, and the products absorb in the region of 240–450 nm. A comparison of the spectral and kinetic properties of the transients indicates that the e aq − and H atom reaction products are different. The reactions of Cl 2 − with these complexes and with PtCl 4 2− occur rapidly (second-order rate constants greater than 1 × 10 8 dm 3 mol −1 s −1) to yield transients absorbing strongly in the region of 230–400 nm. Very similar products are formed through the reactions of trans-dichlorobis(ethylenediamine)platinum(IV) ion with e aq −, H atom, methanol and isopropanol radicals: the associated rate constants range from 6.9 × 10 8 dm 3 mol −1 s −1 for methanol radical to 6.6 × 10 10 dm 3 mol −1 s −1 for e aq −. Evidence is presented to show that these transients are platinum(III) species. Their possible structures and substitutional labilities are discussed.

Chemically Induced Dynamic Electron Polarization. IV. The Photolysis of 1,4-Naphthoquinone

Electron spin resonance emission was studied from the photochemically produced 1,4-naphthosemi-quinone radical in liquid methanol, ethanol, isopropanol, ethylene glycol, and in acetic acid in the presence of 2,6-di-tert-butylphenol. This chemically induced dynamic electron polarization is due to the optically spin polarized triplets of the parent quinone and their subsequent hydrogen abstraction reaction with retention of the polarization in the resultant semiquinone radicals. In the acetic acid–2,6-di-tert-butylphenol system, emission was observed also from the phenoxy counter radical. The magnitude of the polarization at constant microwave power was found to be temperature dependent. The comparison of the photochemical theory and the radical-pair theory is examined in the light of some of the results obtained.

The Pulse Radiolysis of Penicillamine and Penicillamine Disulfide in Aqueous Solution

Aqueous solutions of penicillamine (RSH) and penicillamine disulfide (RSSR) have been pulse irradiated at several pH's and the ensuing reactions studied. The rate constant for the reaction of solvated electrons with penicillamine disulfide decreases from 7.3 × 10−9 M−1 s−1 at pH 7 to 0.8 × 109 M−1 s−1 at pH 10. The first-order rate constant for the decomposition of the resulting radical anion, RSSR−, increases from 1.77 × 106 s−1 at pH 7 to 6.5 × 106 s−1 at pH 10. Both of these pH effects are attributed to deprotonation of the two amino groups of the disulfide which have microscopic pK values of 7.9 and 8.5. The equilibrium constant for the reaction[Formula: see text]is (2.31 ± 0.2) × 102 M−1 at pH 8 but increases to 3.04 × 102 M−1 at pH 7 and decreases to 0.96 × 102 M−1 at pH 9. Measured from the kinetics of the build-up of RSSR−, k−2 = 1.83 × 106 s−1 at pH 8.Decay of RSSR− in the presence of RSH follows second-order kinetics at high dose rates and first-order kinetics at low dose rates. At high dose rates two second-order reactions[Formula: see text]appear to be involved with rate constants of 1.7 × 109 M−1 s−1 and 6.4 × 109 M−1 s−1 respectively at pH 8, At low dose rates the decay appears to be due to a pseudo first-order reaction between RSSR− and H2O, k ~ 2 × 103 s−1, with valine (RH) and penicillamine trisulfide (RSSR) as principal products. These products are obtained in similar yields by gamma radiolysis of penicillamine solutions. At pH 5, the thiyl radical decays by second-order kinetics, 2k = (2.85 ± 0.15) × 109 M−1 s−1.Studies of solutions containing penicillamine and methanol showed that penicillamine repairs methanol radicals very efficiently by hydrogen transfer. k = (1.1 ± 0.1) × 108M−1 s−1. The implications of the results for chemical radioprotection are discussed.

EPR INVESTIGATIONS CONCERNING THE STRUCTURE OF THE ASCORBIC ACID RADICAL IN WATER, ALCOHOL, AND DIMETHYLSULFOXIDE

Abstract— Electron paramagnetic resonance (EPR) spectra of the ascorbic acid radical in water, methanol, ethanol, n‐propanol, and dimethylsulfoxide are reported. The radical was produced by photolyzing ascorbic acid solutions containing acetone. Lines from 13C in natural abundance are observed. Four different 13C‐coupling constants can be distinguished. A comparison of the experimental 1H‐coupling constants with values calculated by the INDO method allows assignment to specific protons in the radical. An effect of solvent on the spectrum is observed and is interpreted in terms of intramolecular hydrogen bonding. Data are presented which indicate that ascorbic acid is able to scavenge alcohol radicals by H‐atom transfer.

Electron spin resonance studies of radical trapping in the radiolysis of organic liquids. I. Evidence for the primary formation of the methoxy radical in methanol

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron spin resonance studies of radical trapping in the radiolysis of organic liquids. I. Evidence for the primary formation of the methoxy radical in methanolJorge A. Wargon and Efrancon WilliamsCite this: J. Am. Chem. Soc. 1972, 94, 22, 7917–7918Publication Date (Print):November 1, 1972Publication History Published online1 May 2002Published inissue 1 November 1972https://doi.org/10.1021/ja00777a040RIGHTS & PERMISSIONSArticle Views124Altmetric-Citations45LEARN 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 (256 KB) Get e-Alerts Get e-Alerts

Studies in homogeneous catalysis: Copper‐phenanthroline complexes as catalysts for the oxidation of methanol

AbstractCopper phenanthroline complexes are catalysts for the oxidation of methanol by oxygen at 30‐45 °.A feature of the reaction is that it shows an induction period unless started with small amounts of H2O2 or cuprous ion. During the reaction the system contains a considerable amount of cuprous complex, the presence of which appears to be an essential condition for the continuation of the oxidation.Hydrogen peroxide, in contrast to other hydroperoxides, rapidly forms cuprous complex when added to a cupric‐phenanthroline system. This reaction probably proceeds via formation of O2−. from HO2− ion and cupric complex. The radical ion \documentclass{article}\pagestyle{empty}\begin{document}\[{\rm O}_{\rm 2}^{-\bullet}\]\end{document} would then abstract a hydrogen atom from methanol (or methoxide) coordinated to cupric‐phenanthroline complex, while simultaneously the cupric ion would abstract an electron from the methanol ligand, thus giving rise to formaldehyde and a proton without the intervention of free methanol radicals. The HO2− ion formed in this reaction would either be reoxidized by cupric complex (chain propagation) or reductively split by a cuprous‐phenanthroline complex (termination).The reactions leading to the hydrogen peroxide‐induced formation of cuprous complex probably constitute an essential part of the mechanism of the copper‐phenanthroline‐catalysed oxidation of methanol by oxygen. In this latter reaction \documentclass{article}\pagestyle{empty}\begin{document}\[{\rm O}_{\rm 2}^{-\bullet}\]\end{document} is supplied by the reaction of cuprous complex with oxygen.