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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.

No MeSH data available.


Related in: MedlinePlus

Activation strain analyses for the oxidative addition of methane and halomethanes to Pd. A dot designates a TS. Energies and bond stretch are relative to reactants.
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fig08: Activation strain analyses for the oxidative addition of methane and halomethanes to Pd. A dot designates a TS. Energies and bond stretch are relative to reactants.

Mentions: So far, we have discussed examples in which the catalyst complex is modified, while keeping methane as the model substrate. Numerous studies have focused on variations in the substrate.2,35–37,41,128 We will discuss the addition of different bonds to bare Pd, that is, besides the methane C–H bonds, also the C–X bonds from the series of halomethanes CH3F, CH3Cl, and CH3Br.41 Initially, one might expect that the barriers for Pd-mediated C–H and C–F activation are rather similar due to the similar bond dissociation energies of these bonds, and that the barriers for activating the weaker CH3–Cl and CH3–Br bonds are lower. Thus, in terms of the activation strain model, these expectations would show up in the strain energy term. Figure 8 confirms these expectations, although only partly.


The activation strain model and molecular orbital theory.

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

Activation strain analyses for the oxidative addition of methane and halomethanes to Pd. 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

fig08: Activation strain analyses for the oxidative addition of methane and halomethanes to Pd. A dot designates a TS. Energies and bond stretch are relative to reactants.
Mentions: So far, we have discussed examples in which the catalyst complex is modified, while keeping methane as the model substrate. Numerous studies have focused on variations in the substrate.2,35–37,41,128 We will discuss the addition of different bonds to bare Pd, that is, besides the methane C–H bonds, also the C–X bonds from the series of halomethanes CH3F, CH3Cl, and CH3Br.41 Initially, one might expect that the barriers for Pd-mediated C–H and C–F activation are rather similar due to the similar bond dissociation energies of these bonds, and that the barriers for activating the weaker CH3–Cl and CH3–Br bonds are lower. Thus, in terms of the activation strain model, these expectations would show up in the strain energy term. Figure 8 confirms these expectations, although only partly.

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