Pseudorotation

The IUPAC (International Union of Pure and Applied Chemistry) defines pseudorotation as "a conformational change resulting in a structure that appears to have been produced by rotation of the entire initial molecule and is superimposable on the initial one, unless different positions are distinguished by substitution or isotopic labeling. No angular momentum is generated by this motion; this is the reason for the term." Formally it refers to symmetrical molecules, although the mechanism is invoked for low-symmetry species also. A small displacement of the atomic positions leads to a loss of symmetry until the symmetric product forms. Although not formally required, pseudorotation normally involves displacements along low-energy pathways.

MX₅ compounds

The Berry mechanism refers to the facile interconversion of axial and equatorial ligand in MX₅ compounds, e.g. D_3h-symmetric PF₅:

Cycloalkanes

The structural dynamics of cycloalkanes can be described as pseudorotations.

References

See also

Bartell mechanism