Pseudorotation, and

UB3LYP theory predicts four minima of Sg which possess Cj, Cjhy O2 d C2 symmetries. At the UMP2 level of theory, no stationary point corresponding to the C2 minimum can be located and two new local minima with and D2 symmetries appear. The Sg conformers are found to be very prone to pseudorotation and are predicted to interconvert readily. For this reason, Cioslowski et al. refer to Sg as a fluxional species [93]. Interestingly, they found that the structures corresponding to local minima are not directly interconvertible. 

The mechanism may involve a nucleophilic attack of the double-bond of the phosphole (17) on the phosphorus atom of phosphorus tribromide to provide intermediates that are stabilized by the loss of proton, pseudorotation, and finally the departure of a bromide anion [48, 49],... 

Ah initio calculations to map out the gas-phase activation free energy profiles of the reactions of trimethyl phosphate (TMP) (246) with three nucleophiles, HO, MeO and F have been carried out. The calculations revealed, inter alia, a novel activation free-energy pathway for HO attack on TMP in the gas phase in which initial addition at phosphorus is followed by pseudorotation and subsequent elimination with simultaneous intramolecular proton transfer. Ah initio calculations and continuum dielectric methods have been employed to map out the lowest activation free-energy profiles for the alkaline hydrolysis of a five-membered cyclic phosphate, methyl ethylene phosphate (247), its acyclic analogue, trimethyl phosphate (246), and its six-membered ring counterpart, methyl propylene phosphate (248). The rate-limiting step for the three reactions was found to be hydroxyl ion attack at the phosphorus atom of the triester. ... 

The conformational dynamics of furanose rings may be described by the mechanisms of pseudorotation and inversion. The former mechanism describes a continuous pathway of interconversion between twenty idealized non-planar (envelope, twist) conformers (Figures 1 and 2) that does not involve the planar form (e.g., - E4 — ... 

Several other sulfur eight-membered heterocycles also exist in boat-chair conformations. 5-Thiacanone (441) has a conformation similar to its oxygen analog (430) and shows barriers to pseudorotation and ring inversion of 28 and 34 kJ mol-1, respectively (80JOC1224). The... 

Recent detailed discussions229,283,284,286,289,290 of the bonding in phosphoranes has usually taken for granted the three-centre, four-electron bond model described above and have concentrated on other related issues of importance in these systems, viz. apicophilicity, pseudorotation and the oxaphosphetanes involved in the Wittig reaction. 

In addition to ab initio quantum simulations of the experimental femtosecond and picosecond pump-probe spectra, traditional continuous-wave (CW) spectra could also be simulated using the time-dependent approach to absorption spectroscopy [13]. The results show that femtosecond/picosecond versus CW spectroscopy is complementary in the present case, the radial and angular pseudorotation and the symmetric stretch are observed, and simulated with preferential sensitivity using CW picosecond, and femtosecond spectroscopy, respectively. 

G. Gerber In our time-resolved experiments on the NaafZ ) state we observe the symmetric stretch even for long delay times. From nanosecond laser and CW laser spectroscopy it is well known that the B state does not decay on femtosecond or picosecond time scales. So I do not see how the decay in the picosecond experiment by Prof. Woste can be understood and how the evolution of the B state symmetric stretch into the pseudorotation and the radial motion can occur. 

Yes, we have considered the possibility of energy transfer from vibration to pseudorotation, and the results give a strong indication for this effect, in agreement with theory. 

Because substitution chemistry at square-planar palladium is dominated by associative processes [48], coordination of the alkene in 22.2 would undoubtedly initially generate penta-coordinate intermediate 22.6. Complex 22.6 could then either evolve to square-planar complex 22.5 by a series of pseudorotations and eventual expulsion of the halide ligand or undergo... 

Corriu and coworkers32 have used compounds of the type 13 to distinguish between two possible routes of ligand exchange—pseudorotation and a dissociative process involving cleavage of the Si—N bond. 

These results show that pseudorotation is to be expected with silicon, and Martin and coworkers39 have shown that it has a lower barrier than pseudorotation involving phosphorus. Thus axial entry, pseudorotation and axial exit, which is generally accepted for phosphorus, is a viable mechanism for silicon. 

TABLE 12. Barriers for pseudorotation and Si—N cleavage in neutral pentacoordinate complexes... 

Figure 8.7. Contour plot of two-dimensional PES (8.24) for pseudorotation and conversion. (a) Hypothetical molecule with two independent double-well vibrations, V=-550.Oq] - 400.Og] + 56.6q + 30.2q. The contours are at 200-cm-1 intervals, (b) V=-...

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