Preferred Label : pseudorotation;
IUPAC definition : Stereoisomerization resulting in a structure that appears to have been produced by
rotation of the entire initial molecule and is superposable on the initial one, unless
different positions are distinguished by substitution, including isotopic substitution.
One example of pseudorotation is a facile interconversion between the many envelope
and twist conformers of a cyclopentane due to the out of plane motion of carbon atoms.
Another example of pseudorotation (Berry pseudorotation) is a polytopal rearrangement
that provides an intramolecular mechanism for the isomerization of trigonal bipyramidal
compounds (e.g. λ5-phosphanes), the five bonds to the central atom E being represented
as e1, e2, e3, a1 and a2. Two equatorial bonds move apart and become apical bonds
at the same time as the apical bonds move together to become equatorial. A related
conformational change of a trigonal bipyramidal structure is described as turnstile
rotation. The process may be visualized as follows. An apical and an equatorial bond
rotate as a pair ca. 120 relative to the other three bonds. (Doubts have been expressed
about the distinct physical reality of this mechanism.);
Origin ID : P04934;
See also
Stereoisomerization resulting in a structure that appears to have been produced by
rotation of the entire initial molecule and is superposable on the initial one, unless
different positions are distinguished by substitution, including isotopic substitution.
One example of pseudorotation is a facile interconversion between the many envelope
and twist conformers of a cyclopentane due to the out of plane motion of carbon atoms.
Another example of pseudorotation (Berry pseudorotation) is a polytopal rearrangement
that provides an intramolecular mechanism for the isomerization of trigonal bipyramidal
compounds (e.g. λ5-phosphanes), the five bonds to the central atom E being represented
as e1, e2, e3, a1 and a2. Two equatorial bonds move apart and become apical bonds
at the same time as the apical bonds move together to become equatorial. A related
conformational change of a trigonal bipyramidal structure is described as turnstile
rotation. The process may be visualized as follows. An apical and an equatorial bond
rotate as a pair ca. 120 relative to the other three bonds. (Doubts have been expressed
about the distinct physical reality of this mechanism.)