Homolytic Reactions Research Articles

The effect of local environment relaxation on elementary homolytic reaction kinetics in glass. Interpretation of the Kohlrausch-Williams-Watts relaxation function

Elementary physical relaxation processes and chemical reactions proceeding under quasimonomolecular conditions are often determined by the fractional exponential law: [R] = [R] 0 exp(− K α t α). Here [R] is the value of a relaxing parameter (concentration), α and K α are constants, ) < α < 1, t is the time. A simple phenomenological model allowing the description of chemical reactions with a rate constant depending on time in accord with the fractional exponential law is given. In the model the constant is assumed to change due to relaxation process running to the vicinity of one of the reagents. The model can be used to describe physical relaxation processes.

ChemInform Abstract: Homolytic Reactions of Ligated Boranes. Part 6. ESR Studies of Dialkyl Sulfide‐Boryl Radicals.

AbstractHydrogen‐atom abstraction by tBuO· or (Me3Si)2N· from the borane complexes (I) gives the corresponding boryl radicals (II), the structures and reactions of which are studied in cyclopropane, Me‐O‐Me/cyclopropane, or oxirane/cyclopropane solution.

ChemInform Abstract: Computer Aids for Organometallic Chemistry and Catalysis

Publisher Summary This chapter describes the flowchart of TrAnsition Metal REACtivity (TAMREAC), placing stress specifically on the matter of interest for the chemist––namely, basic reaction steps. Ionic as well as homolytic reaction steps are also considered. The chapter discusses the difficult problem of deciding which transition metal would best promote a given step, but of course, not definitively settled. The chapter also discusses the possibility of using TAMREAC to propose not-yet-realized new reactions and the results proposed by TAMREAC for selected transformations: ethylene dimerization, ethylene hydroformylation, and allyl-alkyl cross coupling. Mechanistic studies are of great importance in homogeneous catalysis. The active catalyst, often prepared in situ , is not easily isolated and, even when it is, can prove misleading. Although the computer proposed, in two cases at least (dimerization, hydroformylation), innovative mechanistic schemes before the experimental chemist, it provides interesting hints for by-products to be expected in a catalytic transformation.

ChemInform Abstract: Homolytic Reactions of Ligated Boranes. Part 5. Spin‐Trapping and Other Addition Reactions of Ligated Boryl Radicals

The addition reactions of a variety of amine- and phosphine-boryl radicals (L→ḂH2; L = R3N or R3P) with 2-methyl-2-nitrosopropane (MNP), 2,4,6-tri-t-butylnitrosobenzene (TBN), and phenyl-N-t-butylnitrone (PBN) have been studied in benzene solution using e.s.r. spectroscopy. Spin-trapping of the boron-centred radicals by MNP and PBN affords nitroxides, while addition of Me3N→ḂH2 to the ambident TBN yields a mixture of the nitroxide and oxyaminyl adducts, with the latter predominating. Appropriately constituted amine-boryl radicals undergo β-N–C cleavage to give carbon-centred radicals in competition with their spin-trapping by MNP and PBN. In addition to providing mechanistic information, this competition has been used to measure the rate coefficient for spin-trapping of Pri2EtN→ḂH2 by MNP. At 314 K, ktrap is ca. 1.6 × 108 dm3 mol–1 s–1 and thus amine-boryl radicals are trapped more efficiently than alkyl radicals. Attempts to scavenge H3N→ḂH2 were frustrated by the rapid reduction of the spin-traps by ammonia–borane, but this amine-boryl radical did undergo ready addition to alkyl cyanides and isocyanides, to 1,1-di-t-butylethylene, and to 2,6-di-t-butylpyridine as judged by e.s.r. spectroscopy. Addition to cyanides affords transient iminyl radicals H3N→BH2(R)CN˙ which undergo subsequent β-scission at a rate which increases along the series R = Et < Pri < But in parallel with the stabilisation of the departing alkyl radical R˙.

ChemInform Abstract: Homolytic Reactions of Phenyl Tribromomethyl Sulfone and Olefins.

AbstractAddition of the tribromomethyl sulfone (I) to some olefins (II) forms sulfones (III).

ChemInform Abstract: Homolytic Reactions of Ligated Boranes. Part 3. ESR Studies of Radicals Derived from Dialkylamine‐Boranes

ChemInformVolume 18, Issue 8 Physical Organic Chemistry ChemInform Abstract: Homolytic Reactions of Ligated Boranes. Part 3. ESR Studies of Radicals Derived from Dialkylamine-Boranes I. G. GREEN, I. G. GREEN Christopher Ingold Lab., Dep. Chem., Univ. Coll., London WC1H 0AJ, UKSearch for more papers by this authorB. P. ROBERTS, B. P. ROBERTS Christopher Ingold Lab., Dep. Chem., Univ. Coll., London WC1H 0AJ, UKSearch for more papers by this author I. G. GREEN, I. G. GREEN Christopher Ingold Lab., Dep. Chem., Univ. Coll., London WC1H 0AJ, UKSearch for more papers by this authorB. P. ROBERTS, B. P. ROBERTS Christopher Ingold Lab., Dep. Chem., Univ. Coll., London WC1H 0AJ, UKSearch for more papers by this author First published: February 24, 1987 https://doi.org/10.1002/chin.198708060Read the full textAboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume18, Issue8February 24, 1987 RelatedInformation

ChemInform Abstract: Homolytic Reactions of Ligated Boranes. Part 4. ESR Studies of Radicals Derived from Secondary Phosphine‐Boranes

ChemInformVolume 18, Issue 8 Physical Organic Chemistry ChemInform Abstract: Homolytic Reactions of Ligated Boranes. Part 4. ESR Studies of Radicals Derived from Secondary Phosphine-Boranes J. A. BABAN, J. A. BABAN Christopher Ingold Lab., Dep. Chem., Univ. Coll., London WC1H 0AJ, UKSearch for more papers by this authorB. P. ROBERTS, B. P. ROBERTS Christopher Ingold Lab., Dep. Chem., Univ. Coll., London WC1H 0AJ, UKSearch for more papers by this author J. A. BABAN, J. A. BABAN Christopher Ingold Lab., Dep. Chem., Univ. Coll., London WC1H 0AJ, UKSearch for more papers by this authorB. P. ROBERTS, B. P. ROBERTS Christopher Ingold Lab., Dep. Chem., Univ. Coll., London WC1H 0AJ, UKSearch for more papers by this author First published: February 24, 1987 https://doi.org/10.1002/chin.198708061Read the full textAboutPDF 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. Volume18, Issue8February 24, 1987 RelatedInformation

Homolytic reactions of ligated boranes. Part 7. An electron spin resonance study of the t-butyl isocyanide–boryl radical

Photochemically generated alkoxyl or cyclopropyl, but not n-propyl, radicals abstract hydrogen from t-butyl isocyanide–borane (TBIB) to give the corresponding isocyanide–boryl radical ButNC→BH2(1), which has been studied in solution using e.s.r. spectroscopy. The structure and electronic configuration of (1) is discussed in relation to the isoelectronic propargylic radical ButCC–ĊH2. On the basis of qualitative considerations and molecular orbita calculations it is concluded that (1) is probably bent at nitrogen, unlike propargylic radicals which have a linear C–CC–Ċ skeleton, and that the spin population on the β-carbon atom in (1) is much larger than that in ButCC–ĊH2. In contrast with saturated ligated boryl radicals, (1) does not abstract halogen from alkyl bromides, as judged by e.s.r. spectroscopy, and this low reactivity is probably a consequence of unpaired electron delocalisation in the isocyanide–boryl. The t-butyl radical is formed in lower yield along with (1) when dialkyl peroxides are photolysed in the presence of TBIB. β-Scission of (1) is not the source of But˙ and other possible origins are discussed. γ-Radiolysis of polycrystalline TBIB affords But˙ at 77 K, presumably by dissociative electron capture. One-electron reduction of TBIB in a methanol glass at 77 K or by Me2ĊOH in solution also yields But˙.

Homolytic reactions of ligated boranes. Part 6. Electron spin resonance studies of dialkyl sulphide–boryl radicals

Hydrogen-atom abstraction by ButO˙ or (Me3Si)2N˙ from dialkyl sulphide–boranes (R2S→BH3; R = Me or Et) gives the corresponding dialkyl sulphide–boryl radicals (R2S→BH2), the structures and reactions of which have been studied in solution using e.s.r. spectroscopy. The equilibrium geometry at the radical centre in R2S→BH2 appears to be planar or very nearly so, as evidenced by the 11B and Hα hyperfine coupling constants and by the effect of deuterium substitution at boron. Sulphide–boryl radicals undergo ready β-scission [equation (A)], in common with the amine–boryls R3N→BH2 but in marked contrast to, R2S→BH2→ R˙+ RS[graphic omitted]BH2(A) the phosphine–boryls R3P→BH2. Sulphide–boryl radicals abstract halogen rapidly from alkyl bromides and, at 197 K, t-butyl bromide reacts with Me2S→BH2 2.6-times more rapidly than n-propyl bromide. Approximate rate coefficients for the formation and transformation of sulphide–boryl radicals have been obtained from competition experiments. Ab initio molecular orbital calculations at the 6-31G** level for sulphide–, phosphine–, and amine–boryl radicals and for related species provide a basis for interpretation of the experimental results.

ChemInform Abstract: Homolytic Reactions of Tertiary Arsines with Peroxycumyl Radicals.

ChemInform Abstract: Homolytic Reactions of Tertiary Arsines with Peroxycumyl Radicals.

ChemInform Abstract: Small, Strained Bicycloalkyl Radicals and Some Homolytic Reactions Involving Their Patent Bicycloalkanes

ChemInform Abstract: Small, Strained Bicycloalkyl Radicals and Some Homolytic Reactions Involving Their Patent Bicycloalkanes

Homolytic reactions of phenyl tribromomethyl sulfone and olefins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHomolytic reactions of phenyl tribromomethyl sulfone and olefinsD. L. Fields Jr. and H. ShechterCite this: J. Org. Chem. 1986, 51, 17, 3369–3371Publication Date (Print):August 1, 1986Publication History Published online1 May 2002Published inissue 1 August 1986https://doi.org/10.1021/jo00367a023RIGHTS & PERMISSIONSArticle Views233Altmetric-Citations14LEARN 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 (452 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: Homolytic Reactions of Phosphorus‐Organic Compounds. Part 10. Synthesis, Stability and Homolysis of Arylazo‐ and Arylazoalkylphosphonates.

AbstractDie Arylazophosphonate (III) erhält man aus den Diazoniumsalzen (I) und den Phosphiten (II).

Small, strained bicycloalkyl radicals and some homolytic reactions involving their parent bicycloalkanes

Small, strained bicycloalkyl radicals and some homolytic reactions involving their parent bicycloalkanes

Laser flash photolysis–electron spin resonance kinetic studies of homolytic reactions in solution

Laser Flash Photolytic (308 nm) generation coupled with time-resolved e.s.r. spectroscopic detection of radical intermediates has been used to obtain absolute rate coefficients and activation parameters for a number of uni- and bi-molecular homolytic reactions [(A)–(F)] in solution. The results accord well with ButOĊO → But˙+ CO2(A), (EtO)3ṖOBut→ But˙+(EtO)3PO (B), ButO˙+ cyclo-C5H10→ cyclo-C5H9˙+ ButOH (C), ButO˙+ ButOMe → ButOĊH2+ ButOH (D), Me3SiO˙+ cyclo-C5H10→ cyclo-C5H9˙+ Me3SiOH (E), Me3SiO˙+ ButOMe → ButOĊH2+ Me3SiOH (F) those obtained previously for some of these reactions using other techniques. The data for reaction (C) are in excellent agreement with those obtained by laser flash photolysis coupled with optical detection of transients, but differ markedly from results obtained previously by a flash photolysis/e.s.r. technique. The kinetic results for the hydrogen transfers (E) and (F) represent the first absolute rate data for reactions of trialkylsiloxyl radicals. The trimethylsiloxyl radical is more reactive in hydrogen abstraction and also more electrophilic than ButO˙; these differences are attributable to the π-acceptor properties of the Me3Si group.

Competition of homolytic and heterolytic reactions as a way of controlling processes of catalysed oxidation of hydrocarbons

Radical-chain catalyzed liquid-phase oxidation of hydrocarbons by oxygen is important in the industrial production of valuable oxygen-containing derivatives. This study investigates the competition between heterolysis and homolysis during the chromium and vanadium catalyzed decomposition of hydroperoxides.

Homolytic reactions of ligated boranes. Part 4. Electron spin resonance studies of radicals derived from secondary phosphine–boranes

Radicals produced by reaction of photochemically or thermally generated t-butoxyl radicals with dimethyl-, diethyl-, and diphenyl-phosphine–boranes have been studied in solution by e.s.r. spectroscopy. Hydrogen abstraction from R2PH→BH3 appears to yield the phosphinyl–borane radical R2Ṗ→BH3 as the major product, although its e.s.r. spectrum is difficult to detect. Evidence for the competitive formation of an isomeric phosphoranyl radical [R2P(BH2)H]˙ was found for dimethylphosphine–borane. No phosphine–boryl radical R2PH→ḂH2, analogous to R3P→ḂH2 obtained from the reaction of ButO˙ with a trialkylphosphine–borane, was detected. Like the isoelectronic silyl and phosphonyl radicals, R2Ṗ→BH3 abstracts halogen from alkyl bromides and adds readily to alkenes and isocyanides to give alkyl and imidoyl radical adducts, respectively. Spin-trapping of R2Ṗ→BH3 with 2-methyl-2-nitrosopropane or phenyl-N-t-butylnitrone affords the appropriate nitroxides, whilst with 1-nitroso-2,4,6-tri-t-butylbenzene addition takes place exclusively at oxygen to give an oxyaminyl radical.

Homolytic reactions of ligated boranes. Part 5. Spin-trapping and other addition reactions of ligated boryl radicals

The addition reactions of a variety of amine- and phosphine-boryl radicals (L→ḂH2; L = R3N or R3P) with 2-methyl-2-nitrosopropane (MNP), 2,4,6-tri-t-butylnitrosobenzene (TBN), and phenyl-N-t-butylnitrone (PBN) have been studied in benzene solution using e.s.r. spectroscopy. Spin-trapping of the boron-centred radicals by MNP and PBN affords nitroxides, while addition of Me3N→ḂH2 to the ambident TBN yields a mixture of the nitroxide and oxyaminyl adducts, with the latter predominating. Appropriately constituted amine-boryl radicals undergo β-N–C cleavage to give carbon-centred radicals in competition with their spin-trapping by MNP and PBN. In addition to providing mechanistic information, this competition has been used to measure the rate coefficient for spin-trapping of Pri2EtN→ḂH2 by MNP. At 314 K, ktrap is ca. 1.6 × 108 dm3 mol–1 s–1 and thus amine-boryl radicals are trapped more efficiently than alkyl radicals. Attempts to scavenge H3N→ḂH2 were frustrated by the rapid reduction of the spin-traps by ammonia–borane, but this amine-boryl radical did undergo ready addition to alkyl cyanides and isocyanides, to 1,1-di-t-butylethylene, and to 2,6-di-t-butylpyridine as judged by e.s.r. spectroscopy. Addition to cyanides affords transient iminyl radicals H3N→BH2(R)CN˙ which undergo subsequent β-scission at a rate which increases along the series R = Et < Pri < But in parallel with the stabilisation of the departing alkyl radical R˙.

Homolytic reactions of ligated boranes. Part 3. Electron spin resonance studies of radicals derived from dialkylamine–boranes

Liquid-phase e.s.r. studies show that photochemically generated t-butoxyl radicals abstract hydrogen from secondary amine–boranes R2NH→BH3 to give the corresponding amine–boryl radical R2NH→ḂH2 as the kinetically controlled product. Depending on the nature of the N-alkyl groups, the amine–boryl may undergo β-scission or may rapidly abstract hydrogen from the parent amine–borane to give the isomeric aminyl–borane radical R2Ṅ→BH3 which is thermodynamically more stable. Deuterium labelling experiments exclude 1,2-hydrogen atom migration as the mechanism of the isomerisation. The less electrophilic cyclopropyl radical reacts with R2NH→BH3 to yield the aminyl–borane directly by abstraction of hydrogen from nitrogen. In the reactions with t-butoxyl radicals, intermediate amine–boryl radicals may be intercepted by halogen atom transfer from alkyl bromides or by addition to 2-methyl-2-nitrosopropane; with one amine–borane, But(Pri)NH→BH3, the amine–boryl radical was detected directly by e.s.r. spectroscopy. The e.s.r. spectra of the aminyl–borane radicals indicate appreciable hyperconjugative delocalisation of the unpaired electron onto the BH3 group. Ab initio and/or semi-empirical molecular orbital calculations for H3N→ḂH2, H2Ṅ→BH3, and their N-methylated derivatives support the conclusions reached by experiment.

Influence of the pressure on the rate constants of the elementary stages of the homolytic decomposition of organic compounds

1. An equation describing the influence of the pressure on the rate constant of liquid-phase homolytic bond-cleavage reactions has been obtained. 2. A difference in the values of (∂ΔV≠/∂p)p=0/ΔV0≠ in addition and homolytic bond cleavage reactions and in diffusional processes has been found which is explained by the different contribution of the free volume to the volume effect of activation (ΔV0≠). In addition reactions and reactions involving the radical detachment of a hydrogen atom the values of (∂ΔV≠/∂p)p=0/ΔV0≠ are close to one another, and the contributions of the free volume to ΔV0≠ are approximately the same. 3. An equation has been proposed for describing the influence of the pressure on the viscosity of liquids. It has been shown that a linear relationship of free energies with a change in the pressure is inapplicable for this process.