Isomerization difference

It has been already mentioned in passing that indications exist in the literature showing that the 3C isomerization can take place by formation of at least two different 3C complexes, having different activation energies of isomerization, different particle size effects, different responses to alloying, etc. (157, 195-198). The suggestions presented above offer a choice of different complexes for further speculations. However, a definitive description of isomerization mechanisms under different conditions (H2 pressure, temperature, etc.) and with different catalysts (pure metals, alloys, etc.) is not yet possible. 

Several other dienones were observed to be incapable of effective ring closure to 2//-pyran valence tautomers of 459.164,175,387 In other cases cyclic forms such as 460 and 463 were too unstable to be detected,30,164,388 but their existence, although in negligible concentrations, was proved on the basis of the structure of mutually isomerizing different open-chain forms28,99,388 391 or as adducts with tetracyanoethene30 and maleic anhydride.237,392 The com-... 

The presence of such isomeric solvates may account for the asymmetry noted (62, 6) when carrying out the curve resolution of the 90-MHz spectra, but, within the accuracy attainable, the effect is barely significant. There are discrepancies in the values for the intrinsic shifts of the solvated species recorded by all three groups of workers (but differences between successive solvates are more satisfactory). Toma and co-workers calculated (62) the theoretically expected and isomeric differences between successive solvates, obtaining reasonable agreement with observed values (Table V). 

Platt, J. R., Prediction of Isomeric Differences in Paraffin Properties. J. Phys. Chem., 1952 56, 328-336. 

For alkenes, in addition to structural isomerism, geometrical isomerism can also occur. Geometrical isomerism differs only in the arrangement of the atoms in space. 

Class Isomerism.— We have also with the ethers a new case of isomerism different from any we have studied. It will be seen on examining the empirical formulas of ethers that they are the same as the alcohols with an equal number of carbon atoms. 

Platt, J.R. (1952) Prediction of isomeric differences in paraffin properties. J. Phys. Chan., 56, 328—336. 

Stereoconvergent A reaction or reaction sequence is stereoconvergent if stereo-isomerically different starting materials yield the same stereoisomeric product. The sequence may be more specifically labeled either enantioconvergent or diastereoconvergent. 

Water-soluble Pc are obtained by direct sulfonation of the corresponding unsubstituted Pc with fuming sulfuric acid [9] or alternatively by the condensation of various ratios of 4-sulfophthalic acid and phthalic acid (or substituted phthalic acid, phthalonitrile, phthalamide, phthalic anhydride) [10]. In both cases, this yields a mixture of many isomeric differently sulfonated Pc, which require time... 

It is appropriate to start with the definition of isomerism. Different chemical substances (at least by some experimentally detmninable properties) are said to be isomers if and only if they have the same molecular formula. This definition restricts the notion of isomerism to compounds containing covalent bonds (for only then can one speak of molecules and molecular formulas), and possibly also other kinds of bcmds, such as ionic bonds. For example, urea and ammonium cyanate are isomers. Wohler s isomerization of the latter into the former substance (1828) is considered to represent the ezperimmtum cruci in disproving the vitalist theory. The above definition also impUes that two isomeric molecules consist of the same set of atoms bonded differently. 

Indicator variables have also been used to account for other struetural features, e.g. for intramolecular hydrogen bonds, hydrogen bond donor and acceptor properties, ortho effects, cis/trans isomerism, different parent skeletons, different test models, etc. [22, 390]. Some precautions are necessary indicator variables should not describe a single compound (in this case the corresponding group contribution includes the experimental error of this one biological activity value) and the use of indicator variables should be justified from a theoretical point of view otherwise, continuous variables will be mixed with meaningless dummy variables, just to fit the data. 

A volume-conserving mechanism such as hula-twist (H-T) that requires a concomitant twisting of the double bond and the adjacent single bond to accomphsh the double-bond ds-trans isomerization, different from the usual one-bond rotation mechanism. 

Isomerization. Differences between kinetic parameters for intramolecular rearrangement within organotin j5-diketonates of the [Sn(acac)2Ph2] type in bromoform, chloroform, and dichloromethane are small." ... 

Lit C.F. Culberson 1969 Concretin should be 2,4,5-trichloronorliche-xanthone because the other possible isomeres differ in their melting points from the melting point of concretin... 

Here we introduce a further category of isomerism known as stereoisomerism, in which the molecules concerned have the same molecular formula and structural formula, but their atoms are arranged differently in space. There are three types of stereoisomerism — conformational isomerism, cis— trans isomerism and optical isomerism (Figure 20.46). Configurational isomers have permanent Figure 20.46 The different types of isomerism differences in their structural geometry and cannot... 

Scheme 1-231. 4-Chloro-l,2-didehydro-3-(trimethylsilyl)benzene being trapped by two isomerically different aryllithiums to afford four regioisomers.

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