Pseudorotation process, Berry

Berry pseudorotation process, 34 239 Bertrand diagram, 36 3 Bertrand-Gayda Model, 38 176-178 Beryllium... 

C. Comparison of the Turnstile Rotation and Berry Pseudorotation Processes... 

All MO calculations, both semiempirical and ab initio, have demonstrated that the barrier to aZ>3h-C4v-D3h interconversion, the Berry pseudorotation process, is small for acyclic phosphoranes (see also Section 2.1.). Estimates of 1.4 (extended Hiickel MO34 ), 4.8 (ab initio35 ) and 3.5 kcal/mol (CNDO/231 ) have been obtained for PFS. The barrier computed from the ab initio calculation increases to 8.5 kcal/mol if the 3c -orbitals are not included. The turnstile rotation mechanism traverses a much higher energy barrier 10.0 (extended Hiickel MO), 18.1 (ab initio) and 9.1 kcal/mol (CNDO/2). On the basis of these calculations, the Berry pseudorotation mechanism must be the preferred explanation of pentatopal isomerisation in acyclic phosphoranes (see Section 2.1.). 

The intervention of Berry pseudorotation processes was invoked to account for the intramolecular ligand permutation. The authors noted, however, that an isomerization by silicon-oxygen bond breaking cannot be strictly excluded. Indeed, it represents a plausible mechanism since a high activation energy is required (within the expected range for a bond cleavage in these anionic alkoxy-silanes). To eliminate this possibility Farnham and Harlow prepared the spiro-siliconate 196 (eq. [108]). Compound 196, which contains an apical fluorine... 

An ab initio study of the pathway of ligand scrambling of PH4 indicated a turnstile mechanism Involving a TBP-ax transition state with a lower barrier than a Berry pseudorotation process with a C4V transition state [11] see [7]. 

Facile rearrangement of PFg may occur via the Berry pseudorotation process 14.24. After an excursion to the square pyramidal structure and back, axial and... 

The subject of pentacoordinated phosphorus has been considered in depth in two volumes entitled Structure and Spectroscopy and Reaction Mechanisms. The latter volume covers two major topics, namely, a comparison of the Berry pseudorotation process and the turnstile mechanism for explaining the interconversion of rotamers, and the consideration of reactions (from simple to enzymatic) which involve five-coordinate phosphorus intermediates. 

General.—Possible routes for intramolecular rearrangements of four-, five-, and six-co-ordinated structures have been reviewed. The isomerization pathways are represented by Schlegel diagrams these representations are correlated, where relevant, with specific mechanisms such as those discussed by Muetterties, and the Berry pseudorotation process for five-co-ordinate species. 

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