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The activation strain model and molecular orbital theory.

Wolters LP, Bickelhaupt FM - Wiley Interdiscip Rev Comput Mol Sci (2015)

Bottom Line: Using these approaches, a causal relationship is revealed between the properties of the reactants and their reactivity, e.g., reaction barriers and plausible reaction mechanisms.These examples demonstrate how the methodology is applied to different research questions, how results are interpreted, and how insights into one chemical phenomenon can lead to an improved understanding of another, seemingly completely different chemical process.WIREs Comput Mol Sci 2015, 5:324-343. doi: 10.1002/wcms.1221.

View Article: PubMed Central - PubMed

Affiliation: Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM), VU University AmsterdamAmsterdam, The Netherlands; Dipartimento di Scienze Chimiche, Università degli Studi di PadovaPadova, Italy.

ABSTRACT

The activation strain model is a powerful tool for understanding reactivity, or inertness, of molecular species. This is done by relating the relative energy of a molecular complex along the reaction energy profile to the structural rigidity of the reactants and the strength of their mutual interactions: ΔE(ζ) = ΔE strain(ζ) + ΔE int(ζ). We provide a detailed discussion of the model, and elaborate on its strong connection with molecular orbital theory. Using these approaches, a causal relationship is revealed between the properties of the reactants and their reactivity, e.g., reaction barriers and plausible reaction mechanisms. This methodology may reveal intriguing parallels between completely different types of chemical transformations. Thus, the activation strain model constitutes a unifying framework that furthers the development of cross-disciplinary concepts throughout various fields of chemistry. We illustrate the activation strain model in action with selected examples from literature. These examples demonstrate how the methodology is applied to different research questions, how results are interpreted, and how insights into one chemical phenomenon can lead to an improved understanding of another, seemingly completely different chemical process. WIREs Comput Mol Sci 2015, 5:324-343. doi: 10.1002/wcms.1221.

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Related in: MedlinePlus

Activation strain analyses of the SN2 reaction profiles for variation of (a) the leaving group and (b) the nucleophile. A dot designates a TS. Energies and bond stretch are relative to reactants.
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fig10: Activation strain analyses of the SN2 reaction profiles for variation of (a) the leaving group and (b) the nucleophile. A dot designates a TS. Energies and bond stretch are relative to reactants.

Mentions: To arrive at a straightforward relationship between the electronic structure of the reactants and their SN2 reactivity, a number of energy profiles have been investigated while systematically varying one of the reactants.13 In Figure 10(a), we show the first of two representative series that we will discuss, namely the backside nucleophilic attack of Cl− on CH3X substrates, where the leaving group X in the substrate is varied along the halogens F to I. This gives the halomethanes CH3F, CH3Cl, CH3Br, and CH3I, thus resembling the series of C–X bonds in the last example of oxidative addition. Also in these SN2 reactions, the C–X bond is broken by populating the σ*C–X orbital, but now the electrons are being donated from the chloride nucleophile, which approaches the methyl moiety from the back, and not side-on like the Pd metal center in oxidative addition (the original study, Ref 13 also includes such frontside nucleophilic attacks).


The activation strain model and molecular orbital theory.

Wolters LP, Bickelhaupt FM - Wiley Interdiscip Rev Comput Mol Sci (2015)

Activation strain analyses of the SN2 reaction profiles for variation of (a) the leaving group and (b) the nucleophile. A dot designates a TS. Energies and bond stretch are relative to reactants.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696410&req=5

fig10: Activation strain analyses of the SN2 reaction profiles for variation of (a) the leaving group and (b) the nucleophile. A dot designates a TS. Energies and bond stretch are relative to reactants.
Mentions: To arrive at a straightforward relationship between the electronic structure of the reactants and their SN2 reactivity, a number of energy profiles have been investigated while systematically varying one of the reactants.13 In Figure 10(a), we show the first of two representative series that we will discuss, namely the backside nucleophilic attack of Cl− on CH3X substrates, where the leaving group X in the substrate is varied along the halogens F to I. This gives the halomethanes CH3F, CH3Cl, CH3Br, and CH3I, thus resembling the series of C–X bonds in the last example of oxidative addition. Also in these SN2 reactions, the C–X bond is broken by populating the σ*C–X orbital, but now the electrons are being donated from the chloride nucleophile, which approaches the methyl moiety from the back, and not side-on like the Pd metal center in oxidative addition (the original study, Ref 13 also includes such frontside nucleophilic attacks).

Bottom Line: Using these approaches, a causal relationship is revealed between the properties of the reactants and their reactivity, e.g., reaction barriers and plausible reaction mechanisms.These examples demonstrate how the methodology is applied to different research questions, how results are interpreted, and how insights into one chemical phenomenon can lead to an improved understanding of another, seemingly completely different chemical process.WIREs Comput Mol Sci 2015, 5:324-343. doi: 10.1002/wcms.1221.

View Article: PubMed Central - PubMed

Affiliation: Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM), VU University AmsterdamAmsterdam, The Netherlands; Dipartimento di Scienze Chimiche, Università degli Studi di PadovaPadova, Italy.

ABSTRACT

The activation strain model is a powerful tool for understanding reactivity, or inertness, of molecular species. This is done by relating the relative energy of a molecular complex along the reaction energy profile to the structural rigidity of the reactants and the strength of their mutual interactions: ΔE(ζ) = ΔE strain(ζ) + ΔE int(ζ). We provide a detailed discussion of the model, and elaborate on its strong connection with molecular orbital theory. Using these approaches, a causal relationship is revealed between the properties of the reactants and their reactivity, e.g., reaction barriers and plausible reaction mechanisms. This methodology may reveal intriguing parallels between completely different types of chemical transformations. Thus, the activation strain model constitutes a unifying framework that furthers the development of cross-disciplinary concepts throughout various fields of chemistry. We illustrate the activation strain model in action with selected examples from literature. These examples demonstrate how the methodology is applied to different research questions, how results are interpreted, and how insights into one chemical phenomenon can lead to an improved understanding of another, seemingly completely different chemical process. WIREs Comput Mol Sci 2015, 5:324-343. doi: 10.1002/wcms.1221.

No MeSH data available.


Related in: MedlinePlus