Absolute rate constants for the addition of hydroxymethyl radicals to alkenes in methanol solution

Wu, Jie; Fischer, Hanns

doi:10.1002/kin.550270207

Cited by 42 publications

(33 citation statements)

References 51 publications

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“…This may be a result of the Evans–Polany rule42, 43 (in general, an activation energy such as the reaction barrier decreases with the increasing exothermicity of reaction). However, one should be aware of the fact that the correlation factor between Δ H r values and activation energies taken without any constraints on the nucleophilicity or electrophilicity of the reacting radicals is, as a rule, quite low 44. However, it is substantially higher within the group of nucleophilic, electrophilic, and amphiphilic radicals, as long as the corresponding correlation is described with an appropriately refined Evans–Polany relation 8.…”

Section: Resultsmentioning

confidence: 99%

Penultimate unit effects in the free‐radical copolymerization of styrene with acrylonitrile according to theoretical thermochemistry

Cieplak

Megiel

Kaim

2002

J. Polym. Sci. A Polym. Chem.

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Penultimate unit effects in the free‐radical copolymerization of styrene with acrylonitrile were investigated by the consideration of the theoretical thermochemistry of three subsequent propagation steps in the copolymerization process at 298 K and the electronic properties of the relevant reactants. The total energies, zero‐point energies incorporating a 0.96 scale factor, and thermal enthalpy corrections for all optimized structures were computed with the B3LYP density functional theory and the 6‐311G(d,p) basis set. The penultimate unit effect on the enthalpy of reaction for elementary propagation reactions ranged from −1.2 to 2.7 kcal/mol. The enthalpies of elementary copolymerization propagation reactions showed that penultimate unit effects depended not only on the γ substituent itself but also on the terminal unit of the growing radical and the monomer being attached. The exothermicity of the addition of radicals, varying in the penultimate unit for a given monomer, was lower for more polar radicals and smaller Mulliken charges at the radical atom, except for radicals with a CN substituent placed in the γ position when they reacted with acrylonitrile. For the latter system, the repulsive interactions between the CN substituent and nitrile group of the monomer being added contributed to the reaction enthalpy. Almost no penultimate unit effect was detected upon spin distribution at the radical atom, and this probably indicated the absence of the independent implicit penultimate model. The results obtained strengthen the concept of the inseparability of implicit and explicit penultimate unit effects in radical copolymerization. However, it appears that for the styrene–acrylonitrile copolymerization system, the explicit penultimate model prevails over the implicit penultimate model. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3592–3603, 2002

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Section: Resultsmentioning

confidence: 99%

Penultimate unit effects in the free‐radical copolymerization of styrene with acrylonitrile according to theoretical thermochemistry

Cieplak

Megiel

Kaim

2002

J. Polym. Sci. A Polym. Chem.

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“…Therefore, we first discuss experimental data for this simplest situation and select radicals (Figure 4) which allow a case study for the action of enthalpy and polar effects alone. Besides the methyl radical,58 we include the resonance‐stabilized benzyl radical,21, 59 and three other primary radicals, two with an electron‐acceptor substituent (cyanomethyl60 and tert ‐butoxycarbonylmethyl60) and one with an electron‐donor substituent (hydroxymethyl61)), four tertiary species, two with only donor substituents ( tert ‐butyl35, 36a, 62 and 2 ‐ hydroxy‐2‐propyl36b, 63) and two with two donor and one acceptor substituent (2‐ tert ‐butoxycarbonyl‐2‐propyl64 and 2‐cyano‐2‐propyl65). There are also two radicals with stronger electron‐acceptor substitution, namely the cyclic malonyl radical, 2,2 ‐ dimethyl‐4,6‐dioxo‐1,3‐dioxan‐5‐yl, derived from Meldrum's acid,66 and the trifluoroacetonyl radical 64…”

Section: Monosubstituted and 11‐disubstituted Alkenesmentioning

confidence: 99%

Factors Controlling the Addition of Carbon‐Centered Radicals to Alkenes—An Experimental and Theoretical Perspective

Fischer

Radom

2001

Angewandte Chemie Intl Edit

660

364

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The successful exploitation of syntheses involving the generation of new carbon–carbon bonds by radical reactions rests on some prior knowledge of the rate constants for the addition of carbon‐centered radicals to alkenes and other unsaturated molecules, and of the factors controlling them. Two former classical reviews in Angewandte Chemie by Tedder (1982) and by Giese (1983) provided mechanistic insight and led to various qualitative rules on the complex interplay of enthalpic, polar, and steric effects. In the meantime, the field has experienced very rapid progress: many more experimental absolute rate constants have become available, and there have been major advances in the efficiency and reliability of quantum‐chemical methods for the accurate calculation of transition structures, reaction barriers, and reaction enthalpies. Herein we review this progress, recommend suitable experimental and theoretical procedures, and display representative data series for radical additions to alkenes. On this basis, and guided by the pictorial tool of the state‐correlation diagram for radical additions, we then offer a new and more stringent quantification of the controlling factors. Our analysis leads to a partial revision of the previous qualitative rules, and it more clearly exhibits the interplay of the reaction enthalpy effects, polar charge‐transfer contributions, and steric substituent effects on the reaction energy barrier. The various contributions are cast into the form of new, simple, and physically meaningful but non‐linear, predictive equations for the preestimation of rate constants. These equations prove successful in several tests but call for additional theoretical and experimental foundation. The kinetics of related reactions such as polymer propagation, copolymerization, and the addition of radicals to alkynes and aromatic compounds is shown to follow the same principles.

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“…Daher stellen wir zunächst experimentelle Daten für diese einfachste Situation vor und wählen Radikale (Abbildung 4), die Fallbeispiele ausschließlich zur Wirkung von Enthalpie und Polaritätseffekten bieten. Außer dem Methylradikal58 wählen wir das resonanzstabilisierte Benzylradikal21, 59 sowie drei weitere primäre Radikale, wovon zwei einen Elektronenacceptorsubstituenten (Cyanmethyl60 und tert ‐Butoxycarbonylmethyl60) und eines einen Elektronendonorsubstituenten aufweisen (Hydroxymethyl61). Hinzu kommen vier tertiäre Spezies, von denen zwei nur Elektronendonorsubstituenten ( tert ‐Butyl35, 36a, 62 und 2 ‐ Hydroxy‐2‐propyl36b, 63) und zwei je zwei Donor‐ sowie einen Acceptorsubstituenten enthalten (2‐ tert ‐Butoxycarbonyl‐2‐propyl64 und 2‐Cyan‐2‐propyl65).…”

Section: Monosubstitutierte Und 11‐disubstitutierte Alkeneunclassified

Was steuert die Additionen kohlenstoffzentrierter Radikale an Alkene? - Antworten auf experimenteller und theoretischer Grundlage

Fischer

Radom

2001

Angew. Chem.

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Die Addition von kohlenstoffzentrierten Radikalen anAlkene und andere ungesättigte Verbindungen führt unter Abbau von p-Bindungen zur Bildung neuer C-C-s-Bindungen. Diese bedeutende Radikalreaktion wird seit langem in der Polymerchemie angewendet, in neuerer Zeit allerdings auch häufig bei Synthesen kleiner Moleküle. [1±3] Die Geschwindigkeitskonstanten und Selektivitäten variieren be-trächtlich und hängen stark von den Substituenten des Substrats und des Radikals ab. So addiert sich das Methylradikal in flüssigen Lösungen bei Raumtemperatur mit einer Geschwindigkeitskonstante von 4300 m À1 s À1 an Propen. Mit Styrol (2.6 Â 10 5 m À1 s À1 ) und Acrylnitril (5.4 Â 10 5 m À1 s À1 ) läuft die Reaktion etwa hundertmal schneller ab. Das Hydroxymethylradikal, ein einfaches Derivat, addiert sich mehr als zehnmal langsamer an Propen (270 m À1 s À1 ) und Styrol (2.3 Â 10 4 m À1 s À1 ), mit Acrylnitril (1.1 Â 10 6 m À1 s À1 ) hingegen reagiert es merklich schneller als das Methylradikal. Variationen der Geschwindigkeitskonstanten in solchen Gröûenordnungen können über Erfolg oder Misserfolg von Synthesen entscheiden. Daher beruht jede erfolgversprechende Synthesestrategie auf einer gewissen Grundkenntnis der Geschwindigkeitskonstanten derartiger Additionen und der Faktoren, die diese steuern. [2,4] Seit den Anfängen der Radikalchemie wurden diese Faktoren intensiv untersucht, [5] und sie wurden vor einiger

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Absolute rate constants for the addition of hydroxymethyl radicals to alkenes in methanol solution

Cited by 42 publications

References 51 publications

Penultimate unit effects in the free‐radical copolymerization of styrene with acrylonitrile according to theoretical thermochemistry

Penultimate unit effects in the free‐radical copolymerization of styrene with acrylonitrile according to theoretical thermochemistry

Factors Controlling the Addition of Carbon‐Centered Radicals to Alkenes—An Experimental and Theoretical Perspective

Was steuert die Additionen kohlenstoffzentrierter Radikale an Alkene? - Antworten auf experimenteller und theoretischer Grundlage

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