The importance of van der Waals attractions in determining the equilibrium between 1,4- and 1,6-dialkylcyclooctatetraenes

Abstract

The position of equilibrium between the title compounds, which are valence-bond isomers, is governed by the magnitude of the van der Waals' attraction between the two alkyl groups. This is calculated (MMPZ) to favor the 1,6 isomer by less than 0.02 kcal/mol in the case where the two groups are methyl and more than 1.07 kcal/mol in the case where the two groups are tert-butyl.

London Dispersion in Molecular Chemistry—Reconsidering Steric Effects

“…The authors also argue that this is due to dispersive attraction in the 1,6 case 123. 124 These findings are indirectly supported by the notion that molecular mechanics approaches require attractive (electronic) terms to account for the observed equilibria 125…”

“…[123,124] These findings are indirectly supported by the notion that molecular mechanics approaches require attractive (electronic) terms to account for the observed equilibria. [125] If one arrives at the conclusion that intramolecular dispersion interactions can decisively stabilize molecules that otherwise have labile bonds,t hen an extension of this line of thought is to use this "dispersion glue" around reactive . Exemplary depictionso flarge regular s-s and p-p dimers of comparable size: [106] [121]graphanea nd [130]graphene and their association energies per carbon atom at the CCSD(T)l evel of theory.…”

Molecular Systems for the Quantification of London Dispersion Interactions

“…They also observed a solvent dependency of this phenomenon . The exceptional system with its distinct property also raised the interest of theoreticians, who performed computational studies and supported the assumption of Streitwieser, that van der Waals attraction is responsible for the counterintuitive observed stability of the 1,6‐di‐ tert ‐butylcyclooctatetraene 8d …”

London’sche Dispersionswechselwirkungen in der Molekülchemie – eine Neubetrachtung sterischer Effekte

“…[123,124] Diese Schlussfolgerung wird durch die Feststellung gestützt, dass Kraftfeldmethoden attraktive (elektronische) Te rme zur Beschreibung solcher Gleichgewichte bençtigen. [125] Wenn man erst einmal zur Schlussfolgerung gelangt ist, dass intramolekulare LD Moleküle mit ansonsten labilen Bindungen entscheidend stabilisiert, besteht eine Erweiterung dieses Gedankengangs darin, dass man "Dispersionskleber" zur Stabilisierung reaktiver Moleküle (nicht nur deren Bindungen) nutzen kann, sodass diese isoliert und charakterisiert werden kçnnen. Ein Beispiel hierfür kçnnte der so genannte "Korsetteffekt" sein, ein Ausdruck, der geprägt wurde,u md en stabilisierenden Effekt der tBu-Gruppen im Te tratert-butyltetrahedran zu verdeutlichen.…”