Solid state geometric isomerization

Linkage isomerization to the N-bonded isothiocyanato-complex /w j-[Co(acac)2-(NCS)py] was observed to have a half-life of ca. 4 h in chloroform solution. In the solid state linkage isomerization at 341 K has a half-life of ca. 12 h, and this is followed by geometric isomerization with a half-life of ca. 2 days. The latter process is suspected to be catalysed by cobalt(ii). 

Owing to the relative rigidity of the carbon-nitrogen double bond, oximes can exist in two discrete geometrically isomeric forms the E or anti isomer anti-E-217) and the (Z) or syn isomer (syn-Z-217) (equation 70). In solid state, both oximes show high configurational stability and discrete existence. In solution, equilibrium between both isomers is rapidly established, favouring the thermodynamically most stable isomer " ... 

Mott transition, 25 170-172 paramagnetic states, 25 148-161, 165-169 continuum model, 25 159-161 ESR. studies, 25 152-157 multistate model, 25 159 optical spectra, 25 157-159 and solvated electrons, 25 138-142 quantitative theory, 25 138-142 spin-equilibria complexes, 32 2-3, see also specific complex four-coordinated d type, 32 2 implications, 32 43-44 excited states, 32 47-48 porphyrins and heme proteins, 32 48-49 electron transfer, 32 45-46 race-mization and isomerization, 32 44—45 substitution, 32 46 in solid state, 32 36-39 lifetime limits, 32 37-38 measured rates, 32 38-39 in solution, 32 22-36 static properties electronic spectra, 32 12-13 geometric structure, 32 6-11 magnetic susceptibility, 32 4-6 vibrational spectra, 32 13 summary and interpretation... 

The concept of isomerism and isomer counts were used extensively in the development of Werner s theory. They are still important, but on a much more sophisticated level than Werner could have imagined some of the structures which he used are now known to be greatly distorted22 and others are not as simple as he believed. Geometric isomers may exist in one form or another, depending upon the solvent, temperature and other conditions, or they may change their coordination numbers. For example, it has been found that [Co(PEt3)2(NCS)2] is planar in the solid state,... 

The chemical structure of a polymer determines whether it will be crystalline or amorphous in the solid state. Both tacticity (i.e., syndio-tactic or isotactic) and geometric isomerism (i.e., trans configuration) favor crystallinity. In general, tactic polymers with their more stereoregular chain structure are more likely to be crystalline than their atactic counterparts. For example, isotactic polypropylene is crystalline, whereas commercial-grade atactic polypropylene is amorphous. Also, cis-pol3nsoprene is amorphous, whereas the more easily packed rans-poly-isoprene is crystalline. In addition to symmetrical chain structures that allow close packing of polymer molecules into crystalline lamellae, specific interactions between chains that favor molecular orientation, favor crystallinity. For example, crystallinity in nylon is enhanced because of... 

As this position is fixed in space isomeric compounds are possible in which the position of two of the elements or groups linked to the doubly bound carbon atoms are reversed, as in (A) and (B) above. Two stereo-isomeric compounds should therefore be possible according to such a space arrangement and the two isomeric crotonic acids may thus be explained. This kind of stereo-isomerism is termed geometric isomerism. Without taking up in detail the proofs as to which of the two stereo-chemical formulas applies to each of the two crotonic acids, we may simply state the fact, that the properties of the solid or ordinary crotonic acid prove that it must be represented by formula (A), above, in which the methyl and carboxyl groups are 12... 

Acetalation of monohydrazone 60 gave 81-83 (Scheme 16). The H-NMR spectrum of 81 showed a chemical shift difference for the two methyl groups, agreeing with the shift rule of El Ashry (86CC1024). The previous discussion on the isomerism of hydrazones 60 indicated the possibility of their existence in two geometric isomers, particularly in solution. In the solid state, it exists in one form. However, its isopropylidene derivative was found to exist in two forms in the solid state and in solution. Similarly, the cyclohexylidene 82 exists in both forms. On the other hand, benzyli-... 

There are two types of geometrical isomerism associated with octahedral species. In EX2Y4, the X groups may be mutually cis or trans as shown for [SnF4Me2] (1.26 and 1.27). In the solid state structure of [NH4]2[SnF4Me2], the anion is present as the trans- sors tx. 

Cobaltate, tris(l, 2-ethanediamine)-racemization solid state, 466 Cobaltate, tris(oxalato)-racemization solid state, 467 Cobaltates sepulchrates, 22 Cobalt complexes geometric isomerism, 11 hexaammine... 

Geometrical Isomerization. The l,l-Dimethyl-/i -allyl group in [(A -l,l-Me2C8H3)M(PF3)3] (M = Co or Rh) (51) isomerizes to the 1,2-dimethyl isomer on heating to 333 K. The mechanism probably involves a 1,4-hydrogen shift to give (53) with the intermediacy of (52). In the solid state [Co(diphos)2-CI]+ exists in two isomeric forms which equilibrate immediately upon separate... 

---