Degree of stabilization

On account of the high degree of stability of the thiazole ring a large variety of substituted derivatives yield thiazolecarboxylic acids upon oxidation. The oxidation of a methyl group or a substituted methyl group to a carboxyl group has been accomplished in a few instances. 

Like the carbonyl group of aldehydes and ketones the carbon of a C=0 unit m a carboxylic acid is sp hybridized Compared with the carbonyl group of an aldehyde or ketone the C=0 unit of a carboxylic acid receives an extra degree of stabilization from its attached OH group... 

Inductive and resonance stabilization of carbanions derived by proton abstraction from alkyl substituents a to the ring nitrogen in pyrazines and quinoxalines confers a degree of stability on these species comparable with that observed with enolate anions. The resultant carbanions undergo typical condensation reactions with a variety of electrophilic reagents such as aldehydes, ketones, nitriles, diazonium salts, etc., which makes them of considerable preparative importance. 

The mildness of oxalyl chloride permits other sensitive hydroxyl groups ie.g., 5 -OH) to survive without protection. Even the 11 -hydroxyl group has a moderate degree of stability to this reagent. ... 

Electron delocalization stabilizes a molecule. A molecule in which electrons are delocalized is more stable than implied by any of the individual Lewis structures that may be written for it. The degree of stabilization is greatest when the contributing Lewis structures are of equal stability. 

Free rotation around each of the carbon-carbon bonds makes saturated fatty acids extremely flexible molecules. Owing to steric constraints, however, the fully extended conformation (Figure 8.1) is the most stable for saturated fatty acids. Nonetheless, the degree of stabilization is slight, and (as will be seen) saturated fatty acid chains adopt a variety of conformations. 

The differenees in behavior of the eation 145 and its oxygen analog 139 are eaused by differenees in the degree of stabilization of the eharge in the C-1... 

For a long time, this finding was correlated with the observation that substituents at a radical center tend to enhance its stability (Section 1.1.2). This in turn led to the belief that the degree of stabilization conferred on the product radical by the substituents was the prime factor determining the orientation and rate of radical addition to olefins. That steric, polar, or other factors might favor the same outcome was either considered to be of secondary importance or simply ignored. ... 

In principle, the oxidation of proceeds at an electrode potential that is more negative by about 0.7 V than the anodic decomposition paths in the above cases however, because of the adsorption shift, it is readily seen that practically there is no energetic advantage compared to CdX dissolution in competing for photogenerated holes. Similar effects are observed with Se and Te electrolytes. As a consequence of specific adsorption and the fact that the X /X couples involve a two-electron transfer, the overall redox process (adsorption/electron trans-fer/desorption) is also slow, which limits the degree of stabilization that can be attained in such systems. In addition, the type of interaction of the X ions with the electrode surface which produces the shifts in the decomposition potentials also favors anion substitution in the lattice and the concomitant degradation of the photoresponse. 

Experimental studies show that chelating spectator ligands impart a degree of stability to complexes of type 23 (Scheme 13.10) [42]. If monodentate phosphine ligands are used decomposition is rapid at 20°C, however, using dppp no decomposition is detected after 24 h [19]. It was found that the rate of decomposition could be linked to the chelate ring size at 65°C, with dppp decomposition was complete after 6 h, with dppe only a small amount of decomposition occurred after this time [42]. 

In crystalline sodium chloride, sodium and chlorine atoms are arranged at the corners of cubes in such a manner that each chlorine atom is immediately adjacent to only sodium atoms and each sodium atom is immediately adjacent to only chlorine atoms. This arrangement gives a high degree of stability because of the large number of bonds between unlike or oppositely charged atoms. The common habit is the cube. 

If the intermediate compound XZ is very unstable, Z cannot serve as a catalyst, while if it is very stable then the reaction stops. The intermediate compound XZ must have the right degree of stability for the catalyst to be effective. It must be borne in mind that the catalyst will accelerate the forward as well as the reverse reactions to the same extent, so that the ratio of the specific rate constants for the forward (kf) the backward (kb) reactions will not be affected. As an example a gaseous reaction between sulfur dioxide and oxygen to yield sulfur trioxide may be considered. The reaction, which can be represented by the equation... 

Radicals, of varying degrees of stability, involving atoms other than carbon—heteroradicals—were also recognised. Thus it was discovered in 1911 that on warming N,N,N, N -tetraarylhydrazines, e.g. (8), in non-polar solvents resulted in the development of a green colour due to the radical (9) ... 

Pascual J.A., Hernandez T., Garcia C., Ayuso M. Carbon mineralization in an arid soil amended with organic wastes of varying degrees of stability. Commun Soil Sci Plant Anal 1998 29 835-846. 

The complex and sometimes competing issues of solubility, stability, and reactivity of reagents designed for purely aqueous POCL were addressed by Barnett et al. [21,22], who furthered the development of the trifluormethylsulfonyl-substituted oxamide class of reagents. They prepared disulfonic acid functionalised oxamides (see Fig. 4), which were found to possess a considerably improved degree of stability at both ambient and low temperature when compared to METQ, in addition to showing some promise as potential reagents in analytical applications. 

All things considered, the best a priori guess would be that carbanions of any degree of stability will be incapable of retaining optical asymmetry but capable of retaining a cis or trans configuration at a double bond. Neither expectation is contradicted by the available facts. 

It is fortunate that in many cases we are able to show that there are stable substances (radicals, ions, etc.) of the same type as the hypothetical intermediate and that these more stable or more accessible substances actually have the chemical properties required of the hypothetical ones. Observable radicals and ions have a great variety of degrees of stability, depending on their structures. The extrapolation to the properties of the hypothetical intermediate is therefore a continuous one. 

---