Van der Waals strain
Van der Waals strainisstrainresulting fromVan der Waalsrepulsion when twosubstituentsin amoleculeapproach each other with a distance less than the sum of theirVan der Waals radii. Van der Waals strain is also calledVan der Waals repulsionand is related tosteric hindrance.[1]One of the most common forms of this strain iseclipsing hydrogen,inalkanes.
In rotational and pseudorotational mechanisms
[edit]In molecules whosevibrational modeinvolves a rotational or pseudorotational mechanism (such as theBerry mechanismor theBartell mechanism),[2]Van der Waals strain can cause significant differences inpotential energy,even between molecules with identical geometry. PF5,for example, has significantly lower potential energy thanPCl5. Despite their identicaltrigonal bipyramidal molecular geometry,the higher electron count ofchlorineas compared tofluorinecauses a potential energy spike as the molecule enters its intermediate in the mechanism and the substituents draw nearer to each other.
See also
[edit]References
[edit]- ^Organic chemistry4th. Ed., Morrison and BoydISBN0-205-05838-8
- ^ Rzepa, Henry S.;Cass, M.E.; Hii, K.K."Mechanisms that Interchange Axial and Equatorial Atoms in Fluxional processes".Retrieved2008-03-27.
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