Chemical stability isomerization

The effects of temperature on carotenoid content can be considered from three perspectives (1) evaluation of stability or retention of carotenoids, (2) study of the chemical changes (isomerization, oxidation, epoxy-furanoid rearrangement), and (3) their effects on the nutritional value and other carotenoid actions in humans. The first two topics are discussed in the following sections. The third is presented in Section 3.2.4.1 of Section 3.2. 

In a similar manner, of the isomeric trinitrobenzenes, only the symmetrical 1,3,5-isomer shows sufficient chemical stability for use as an explosive. Even so, the aromatic ring of 1,3,5-trinitrobenzene is highly electron deficient and reaction with alkali metal carbonates or bicarbonates in aqueous boiling methanol yields 3,5-dinitroanisole. Unsymmetrical isomers of trinitrobenzene are much more reactive than the 1,3,5-isomer, with only relatively mild conditions needed to effect the displacement of their nitro groups. ... 

A.T. Nielsen et al, Reduction and Ammonoly-sis Products Derived from Isomeric Trinitrotoluenes. Synthesis and Chemical Stability of the Aminodinitrotoluenes , NWC-TP-5933, NavalWeapCenter, China Lake (1977)... 

Some of the chemical concepts with little or no quantum-mechanical meaning outside the Bohmian formulation but, well explained in terms of the new interpretation, include electronegativity, the valence state, chemical potential, metallization, chemical bonding, isomerism, chemical equilibrium, orbital angular momentum, bond strength, molecular shape, phase transformation, chirality and barriers to rotation. In addition, atomic stability is explained in terms of a simple physical model. The central new concepts in Bohmian mechanics are quantum potential and quantum torque. 

Chemical stability due to hydrolysis, oxidation, deamination, isomerization, racemization, epimerization, p elimination, and disulfite exchange... 

Considering chemical stability, even alterations at single amino acids or the peptide bond can be detrimental [6], Chemical reactions having an impact on protein stability include hydrolysis of the peptide bond, deamidation, oxidation, p-elimina-tion, isomerization, and disulfide bond breakage and formation. The extent to which they occur is mainly influenced by the temperature and pH value of the solution [24], Bearing in mind that proteins react sensitively to the above-mentioned environmental conditions, preparation procedures for protein pharmaceuticals have to be chosen very carefully to preserve protein integrity and functionality. 

The most important use of XV is its telomerization with fluoride ion to give a linear hydrofluoroacyl fluoride (XVI), that is fluorinated with elemental fluorine to give a linear perfluorinated polyether (XVIII), which is sold by Daikin as Demnum (Eq 13.18). Note that Demnum and Krytox are isomeric materials. In general, their properties are quite similar, but there are subtle differences in physical properties and in chemical stability in tribological applications. 

CNMR using CO group resonances to study composition, chemical stability and cisoid-transoid isomerism... 

The eomposition of PAHs in association with airborne particles depends significantly on the emission sources. PAH concentration ratios can be used to identify possible emission sourees combustion of vegetal biomass or combustion of fossil fuels. [62]. These ratios are usually restricted to PAHs with equal molecular weights, which are normally present in combustion processes due to their chemical stability [63-65]. Table 4 shows several isomeric ratios of PAHs used to distinguish among combustion sources. 

The interest in azacyclooctatetraenes is mainly due to their structural similarity to cycloocta-tetraene.1 3 Most synthetic efforts have concentrated on a comparison of the unusual chemical and physical properties of cyclooctatetraene with its aza analogs. Besides studies concerning the aromaticity, the primary focus of much work has concerned the stability of the eight-membered ring and its valence isomerization. 

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