Relative Thermal Stability

Reaction involves more than a single step. The relative thermal stabilities of the hexammine salts, as determined by the temperatures of onset of the reaction, are Cl" > Br for the cobalt compounds but Br" > Cl" > I" for the chromium compounds. When X = NOi, rapid oxidation developed into an exothermic explosive reaction of both the Cr and the Co salts. 

Fig Relative thermal stability of polymers as determined by weight loss on heating at 5°C/min in nitrogen in thermogravimetric analysis. 

Arguments similar to those stated above can be used to explain the relative chemical inertness of fluoropolymers. Consider the reactivity of alkanes vs. perfluoroalkanes as shown in Table 4.2 (abstracted from Sheppard and Sharts Statistically, FA based materials will have many more types of bonds, in addition to C—F, than fluoropolymers. These bonds will be subject to the same chemical fate during assault by aggressive reagents as bonds in their hydrocarbon counterparts. Similar reasoning can be used to explain the relative thermal stability of FAs compared to fluoropolymers. Thus, incorporation of perfluoroalkyl groups will not make the modified material less stable than the native one. 

Annular prototropy is not of great importance for small heterocycles. However, it should be mentioned that 1-azirine (2) is much more stable than its antiaromatic 2-isomer (3). By analogy, antiaromaticity is certainly a key factor determing instability of lH-azepines which have never been observed. Thus, demethoxycarbonylation of methyl-3,6-di-r-butylazepine-l-carboxylate (46) by DBU gives a mixture of the corresponding 2H-, 3H-, and 4//-azepines in the approximate ratio 13 56 1 (Scheme 9) (94JCS(P1)1753). The distribution of the azepine isomers is proportional to their relative thermal stabilities as they interconvert via allowed 1,5-hydrogen shifts. 

Relative Thermal Stability of Selected Polymers Based on the Temperature at Which Their Half-Life Th Is 30 min... 

In order to study the influence of a mutation in position 218 further, Asn218 was changed genetically to Asp, Cys, Ala. The relative thermal stabilities of these variants are Ser>Asp>Asn>Cys>Ala, as expected Ser forms the optimum hydrogen bonds Asp is better than Asn because of the negative charge, but not... 

At room temperature and atmospheric pressure, the relative thermal stability of the four modifications has been determined by solvent-mediated transformations and thermal analysis to be > y > Q -hemihydrate > p (Foltz et al. 99Aa,b Foltz 1994). Of the anhydrate materials is indeed the most dense as expected from this ordering (see Section 2.3), but in contradiction to the expected correlation between density and relative stability p is more dense than y (Nielsen et al. 1998). 

In view of the relative thermal stabilities of the oxides (Rh203 > PdO Pt02), it is not surprising that under oxidizing conditions and at temperatures higher than 870 K, metallic Pt particles exist in combination with Rh oxide 132,133) and that PdO crystallites separate from Pt crystallites in Pd-Pt alloys in the temperature range 670-870 K 134). A more complicated behavior was found for Pd-Rh 135). 

Calculated from the activation parameters arbitrarily at 20°C for sakes of comparing their relative thermal stabilities. 

Figure 10.8. Relative thermal stability of polymers by TGA (6). PVC = polyvinylchloride PMMA = polymethylmethacrylate PI = polyimide...

The qualitative agreement of the autoignition values with relative thermal stability can be illustrated with the compounds acetone and acetaldehyde. Acetone has an autoignition temperature of 538°C, whereas the value for acetaldehyde is... 

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