// Workers AI · dad joke modeWhat did pseudorotation say? "I'm just spinning a fake story.
In chemistry, a pseudorotation is a set of intramolecular movements of attached groups (i.e., ligands) on a highly symmetric molecule, leading to a molecule indistinguishable from the initial one. The International Union of Pure and Applied Chemistry (IUPAC) defines a pseudorotation as a "stereoisomerization resulting in a structure that appears to have been produced by rotation of the entire initial molecule", the result of which is a "product" that is "superposable on the initial one, unless different positions are distinguished by substitution, including isotopic substitution".[1]
Well-known examples are the intramolecular isomerization of trigonal bipyramidal compounds by the Berry pseudorotation mechanism, and the out-of-plane motions of carbon atoms exhibited by cyclopentane, leading to the interconversions it experiences between its many possible conformers (envelope, twist).[2] Note that no angular momentum is generated by this motion: otherwise a macroscopic sample would heat-up by itself, as an additional angular momentum would increase the population of certain rotational states which would increase the overall thermal energy, comparable to heating in a microwave oven. As this is not observed and would also create a perpetuum mobile of first kind, there can be no angular momentum change involved. In these and related examples, a small displacement of the atomic positions leads to a loss of symmetry until the symmetric product re-forms (see image example below), where these displacements are typically along low-energy pathways.[citation needed] The Berry mechanism refers to the facile interconversion of axial and equatorial ligand in MX5 types of compounds, e.g. D3h-symmetric PF5 (shown).[1][3] Finally, in a formal sense, the term pseudorotation is intended to refer exclusively to dynamics in symmetrical molecules, though mechanisms of the same type are invoked for lower symmetry molecules as well (otherwise stereoisomers would be observable for the affected compound if it is “asymmetrical enough”).
See also
[edit]References
[edit]- 1 2 "Pseudorotation". The IUPAC Compendium of Chemical Terminology. 2014. doi:10.1351/goldbook.P04934.
- ↑ Dragojlovic, Veljko (2015). "Conformational analysis of cycloalkanes" (PDF). Chemtexts. 1 (3): 14–15. Bibcode:2015ChTxt...1...14D. doi:10.1007/s40828-015-0014-0. S2CID 94348487.
- ↑ Couzijn, Erik P. A.; Slootweg, J. Chris; Ehlers, Andreas W.; Lammertsma, Koop (2010). "Stereomutation of Pentavalent Compounds: Validating the Berry Pseudorotation, Redressing Ugi's Turnstile Rotation, and Revealing the Two- and Three-Arm Turnstiles". Journal of the American Chemical Society. 132 (51): 18127–18140. Bibcode:2010JAChS.13218127C. doi:10.1021/ja105306s. PMID 21082808.
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