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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 of the model substitution and elimination reaction profiles under (a) basic (OH− + CH3CH2OH) and (b) acidic (H2O + CH3CH2OH2+) conditions. A dot designates a TS. Energies and bond stretch are relative to reactants.
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fig11: Activation strain analyses of the model substitution and elimination reaction profiles under (a) basic (OH− + CH3CH2OH) and (b) acidic (H2O + CH3CH2OH2+) conditions. A dot designates a TS. Energies and bond stretch are relative to reactants.

Mentions: In a recent study,19 we compared the SN2 energy profiles for OH− + CH3CH2OH and H2O + CH3CH2OH2+ (see Figure 11, blue lines). This constitutes the effect of changing simultaneously from a model system with a good nucleophile and a poor leaving group (OH−) to a model system with a poor nucleophile and an excellent leaving group (H2O), by simply protonating both moieties. In agreement with the results discussed above, going from the OH− to the poorer H2O nucleophile weakens the interaction energy significantly, but this effect is almost entirely compensated for by the softer strain energy term, as simultaneously the leaving-group ability is enhanced from CH3CH2OH to CH3CH2OH2+. The net result is only a small difference in reaction barrier, with the barrier for the protonated reaction being a few kcal mol−1 lower.


The activation strain model and molecular orbital theory.

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

Activation strain analyses of the model substitution and elimination reaction profiles under (a) basic (OH− + CH3CH2OH) and (b) acidic (H2O + CH3CH2OH2+) conditions. 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

fig11: Activation strain analyses of the model substitution and elimination reaction profiles under (a) basic (OH− + CH3CH2OH) and (b) acidic (H2O + CH3CH2OH2+) conditions. A dot designates a TS. Energies and bond stretch are relative to reactants.
Mentions: In a recent study,19 we compared the SN2 energy profiles for OH− + CH3CH2OH and H2O + CH3CH2OH2+ (see Figure 11, blue lines). This constitutes the effect of changing simultaneously from a model system with a good nucleophile and a poor leaving group (OH−) to a model system with a poor nucleophile and an excellent leaving group (H2O), by simply protonating both moieties. In agreement with the results discussed above, going from the OH− to the poorer H2O nucleophile weakens the interaction energy significantly, but this effect is almost entirely compensated for by the softer strain energy term, as simultaneously the leaving-group ability is enhanced from CH3CH2OH to CH3CH2OH2+. The net result is only a small difference in reaction barrier, with the barrier for the protonated reaction being a few kcal mol−1 lower.

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