Das Distortion/Interaction‐Activation‐Strain‐Modell zur Analyse von Reaktionsgeschwindigkeiten

Abstract

Das Activation‐Strain‐ oder Distortion/Interaction‐Modell ist ein Instrument zur Analyse von Aktivierungsbarrieren und damit von Reaktionsgeschwindigkeiten. Für eine bimolekulare Reaktion ergibt sich die Aktivierungsenergie aus der Summe der Energien, die für die Deformation der Grundzustandsgeometrie der Reaktanten benötigt wird, um die Geometrie des Übergangszustands anzunehmen, plus der Wechselwirkungsenergie zwischen diesen deformierten Reaktanten. Die mit der Deformation assoziierte Energie wird “activation strain” (Aktivierungsspannung) oder “distortion energy” (Deformationsenergie) genannt. Diese Energie bildet den Hauptbeitrag zur Aktivierungsbarriere. Der Übergangszustand wird erreicht, wenn die stabilisierende Wechselwirkung die Aktivierungsspannung überwindet. Die Verlaufsanalyse dieser Energien gibt Einblicke in die reaktivitätsbestimmenden physikalischen Faktoren. Anwendungsbeispiele für das Modell sind die Analyse von Substitutions‐ und Eliminierungsreaktionen sowie Cycloadditionen.

Effect of an α‐Methyl Substituent on the Dienophile on Diels‐Alder endo:exo Selectivity

“…In order to gain a deeper understanding of the effect of the α-methyl substituent, we performed an activation strain (ASM) -distortion/interaction analysis [12] of the reaction profiles. The obtained activation strain diagrams (ASDs) are shown in Figure 2.…”

“…The computed reaction profiles were analyzed using the activation strain (ASM) -distortion/interaction model [12] developed by Bickelhaupt -Houk, respectively, modified to include solvation effects. [31] Within this framework, the solution-phase energy profile ΔE solution (ζ) is decomposed along the reaction coordinate ζ into the energy of the solute ΔE solute (ζ), the reaction system in vacuum but with its geometry in solution, plus the solvation energy ΔE solvation (ζ) [Eq.…”

“…In 2014, Fernández and Bickelhaupt [11] reevaluated the 1 + 2 reaction by using the activation strain model (ASM, also known as distortion / interaction model) [12] in combination with the energy decomposition analysis (EDA). [13] The authors found that "the interaction term [14] appears to be not at all decisive for the endo selectivity."…”

Low‐Temperature Intramolecular [4+2] Cycloaddition of Allenes with Arenes for the Synthesis of Diene Ligands

“…To gain additional insight, we analyzed the energetic profiles of these nine reactions using the activation strain model. [35] Initially,w es peculated that the bulky tert-butyl groups in R 1 could diminish the planarity of the benzene ring, lowering the distortion energy and making it easier to break aromaticity.However,the calculation results showed that the presence of the bulky substituents in R 1 causes energetically favorable dispersive interactions at longer C À Cd istances, whereas no major difference in strain energy was observed (Figure 1). This results in an earlier, lower energy transition state for the tert-butyl containing variant relative to methyl or hydrogen.…”

Chiral Phosphoric Acid Dual‐Function Catalysis: Asymmetric Allylation with α‐Vinyl Allylboron Reagents

“…As shown in Figure 5, the energy of optimized transition state TS-9 is 2.7 kcal mol À1 lower than that of TS-11 (si-face attack to give ent-6a), in good agree- To better elucidate the origin of observed enantioselectivity,w ep erformed ad istortion/interaction analysis of the transition states. [37] Thes tructures of TS-9 and TS-11 are divided into three fragments:c atalyst (R)-A,b enzaldehyde, and the allylboronate ( Figure 5). Thec alculated distortion energy of TS-11 is 2.1 kcal mol À1 lower than that of TS-9, while the interaction energy of TS-11 is 4.6 kcal mol À1 higher than that of TS-9.T herefore,t he overall energy of TS-11 is 2.5 kcal mol À1 higher than TS-9 based on the distortion/ interaction analysis model, indicating transition state TS-9 is more favorable than TS-11.…”