Also contains definitions of: Berry pseudorotation, turnstile rotation
Stereoisomerization resulting in a structure that appears to have been produced by rotation of the entire initial molecule and is @S06144@ 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 @P04755@ that provides an @I03130@ mechanism for the @I03295@ of trigonal bipyramidal compounds (e.g. \(\lambda ^{5}\)-@P04548@), the five bonds to the @C00930@ E being represented as \(\text{e}^{1}\), \(\text{e}^{2}\), \(\text{e}^{3}\), \(\text{a}^{1}\) and \(\text{a}^{2}\). Two @A00415@ bonds move apart and become @A00415@ bonds at the same time as the apical bonds move together to become @E02174@.
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 @E02174@ 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.)
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2215 [Terms] [Paper]