Diagonal twist

Diagnostic agents classification, 36 6-7 inorganic, 36 5-6 Diagonal twist, 34 253-254 Dialkyl alkyl phosphonates, in liquid-liquid extraction, 9 29... 

By using P, Pt and NMR, it has been found that Pt(GePh3)(HgGePh3)(PPh3)2 is fluxional. Activation parameters are measured, and it is proposed that the intramolecular rearrangement occurs via a diagonal twist. ... 

N.m.r. spectroscopy has been used to study enantiomeric inversions of a series of tetrahedral chelates of zinc(ii), cadmium(ii), and lead(ii). The rates of inversion depend on the nature of the metal, the donor atoms, and the structure and substituents of the chelate rings. An intramolecular diagonal-twist mechanism is suggested. Rapid complex formation kinetics between zinc(ii) and the glycine zwitterion and pada (pyridine-2-azo-p-dimethylaniline) have been studied using relaxation methods. 

For explicitness, let us assume that off-diagonal disorder is caused by chain twists, which randomly diminish the overlap between the n-orbitals of neighboring carbon atoms (see Fig. 3-7). The electron hopping amplitudes that depend both on the interatomic distances and on the relative orientation of the electronic orbitals on neighboring atoms can then be written in the form ... 

Eaton and Leipzig chose to resolve racemic trishomocubanone by reaction with /-ephedrine and separation of the diastereomers by fractional crystallization. Subsequent acid hydrolysis delivered the enantiomeric ketones Successive removal of a diagonal CHj bridge from —)-451 furnishes (—)-ditwist-brendane (Cj symmetry) 454) and (—)-twist-brendane C symmetry) 455). Also,... 

All other matrix elements of the perturbations, Vso and Fvlb, between the zero-order states, are taken to be zero. That is, we neglect the direct coupling of the singlet with the manifold of twisted triplets, and assume that all the zero-order states have been chosen such that there are no nonvanishing diagonal matrix elements of Fao or Fvlb, nor any vibronic interactions within the set of closely-spaced states, />. ... 

The point groups V d have, in addition to the axes defining Vn, n diagonal planes Od which bisect the angles between successive twofold axes. The ad and C2 axes imply that there is also an S2n and, if n is odd, a center of symmetry Molecules of T>2d symmetry have the shape of two equivalent halves twisted b 90°, for example, allene and spiran shown here ... 

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