Anion carboxy stabilized

Because of resonance stabilization of the anion, a tet-nazolyl moiety is often employed successfully as a bioisosteric replacement for a carboxy group. An example in this subclass is provided by azosemide (27). Benzonitrile analogue is prepared by phosphorus oxychloride dehydration of the corresponding benzamide. Next, a nucleophilic aromatic displacement reaction of the fluorine atom leads to The synthesis concludes with the 1,3-dipolar addition of azide to the nitrile liinction to produce the diuretic azosemi de (27). ... 

Such nucleophilic displacements are likely to be addition-elimination reactions, whether or not radical anions are also interposed as intermediates. The addition of methoxide ion to 2-nitrofuran in methanol or dimethyl sulfoxide affords a deep red salt of the anion 69 PMR shows the 5-proton has the greatest upfield shift, the 3- and 4-protons remaining vinylic in type.18 7 The similar additions in the thiophene series are less complete, presumably because oxygen is relatively electronegative and the furan aromaticity relatively low. Additional electronegative substituents increase the rate of addition and a second nitro group makes it necessary to use stopped flow techniques of rate measurement.141 In contrast, one acyl group (benzoyl or carboxy) does not stabilize an addition product and seldom promotes nucleophilic substitution by weaker nucleophiles such as ammonia. Whereas... 

Other electron-withdrawing substituents which have been used to stabilize cyclopropyl anions are the acyl, ° carboxy, ° nitro, and isocyanide groups. With one exception, the first three were unsuccessful, partly because other reactions took place. Thus, cyclopropanecarboxylic acid undergoes dimerization to l-(cyclopropylcarbonyl)cyclo-propanecarboxylic acid, and this reaction predominates above room temperature. When ni-trocyelopropane was treated with base spontaneous dimerization oceurred, yielding mixtures of 1-nitro-l-nitrosobicyclopropyland l,l -dinitrobicyclopropyl. The yields of the two products were dependent on the workup procedure employed. 

Figure 14.16. Stability of various types of thickener over different pH ranges MC, methyl cellulose HEC, hydroxy ethyl cellulose CMC, carboxy methyl cellulose , includes blends with anionics...

A combinatorial coating of PEG and cationic WSC, on PLA nanoparticles, has yielded greatly prolonged circulation time for the nanocarriers in vivo. In contrast to PLA nanoparticles treated with PEG or WSC alone, PEG and WSC synergisticaUy provided a strong inhibition of macrophage uptake and extended the circulation half-life up to 63.5 h, with concomitant reduced liver sequestration. This ty2 value was much longer than that of control PEG/PVA nanoparticles (1.1 h) as well as that of PLA nanoparticles stabilized with PEG/CPCTS (anionic N-carboxy propionyl... 

The reason for this enhanced acidity of the carboxyl group in an a-amino acid is the inductive effect of the neighboring aminium cation, which helps to stabilize the carboxy-late anion formed when it loses a proton. Loss of a proton from the carboxyl group in a cationic a-amino acid leaves the molecule electrically neutral (in the form of a dipolar ion). This equilibrium is shown in the red-shaded portion of the equation below. 

Nonionic polymers, which can be used as stabilizers are, e.g., starches, polyvinyl alcohols, and polyacrylamides. Nonionic polymers work as protective colloids their mechanism of stabilization is Steric stabilization. Carboxy methyl cellulose bears a small anionic charge along the chain. However, it is often considered to act as a protective colloid. Actually, carboxy methyl cellulose can be considered to use both its protective colloid properties and its charge in stabilizing, thus acting as an electrosteric stabihzer. 

In Summary Phenols exist in the enol form because of aromatic stabilization. They are named according to the rules for naming aromatic compounds explained in Section 15-1. Those derivatives bearing carboxy groups on the ring are called hydroxy-benzoic acids. Phenols are acidic because the corresponding anions are resonance stabilized. 

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