Substituents acidic functions

The transformation of the hydrophobic periphery composed of bromo substituents into a hydrophilic wrapping of carboxylic acid functions was achieved by reacting 31 with (i) n-butyllithium and (ii) carbon dioxide. The polymer-analogous transformation provides water soluble, amphiphilic derivatives of 31 which constitute useful covalently bonded unimolecular models for micellar structures. 

The first step was found to be a fast pre-equilibrium (Scheme 12-8). The dependence of the measured azo coupling rate constants on the acidity function and the effect of electron-withdrawing substituents in the benzenediazo methyl ether resulting in reduced rate constants are consistent with a mechanism in which the slow step is a first-order dissociation of the protonated diazo ether to give the diazonium ion (Scheme 12-9). The azo coupling proper (Scheme 12-10) is faster than the dissociation, since the overall rate constant is found to be independent of the naphthol con-... 

Reactions with anhydrides afford interesting compounds having a carboxylic acid function (Table 26, entries 5 and 7 and Figure 40). It is notable that in the case of succinic anhydride, if the reaction is carried out at 25 °C, only one substitution occurs on the nitrogen atom, if the temperature is increased to 180 °C, there is a second substitution giving rise to a heterocyclic substituent (Table 26, entries 5-8). 

Soluble PPPs 6 are known today that contain, not only alkyl substituents, but also alkoxy groups, as well as ionic side groups (carboxy and sulfonic acid functions) [21], which are able to form PPP polyelectrolytes. 

The transformation of the terminal bromo substituents to carboxylic acid functions with (i) n-butyl lithium (ii) carbon dioxide, provides water soluble derivatives of 47 which are interesting as models for unimolecular micelles. 

A drawback of the Heck-type reaction is that it is not strictly regioselective [119]. Depending on the substituents >1% of 1,1-diarylation is observed. Soluble 2,5-dialkoxy-PPVs 63 or 2-phenyl-PPV PPPV 93, without 1,1-diarylated moieties, were synthesized by Heitz et al. in a Suzuki-type cross coupling of substituted 1,4-phenylenediboronic acids and fran5-l,2-dibromoethylene, catalyzed by Pd(0) compounds [120]. However, about 3% of biaryl defect structures are observed in the coupling products (M up to 12,000), resulting from homocoupling of boronic acid functions. 

Figure 13.10.2 The structure of a beta hydroxy acid, a substituted carboxylic acid in which the hydroxyl substituent is attached to the beta position, i.e., at a carbon atom two positions away from the carboxylic acid functionality.

Modification of Substituents and Functional Groups of Cyclic Nitronates At an ambient temperature, four-membered cyclic nitronate containing the chloronitromethyl group at the C-3 atom is gradually transformed into the corresponding acid chloride even under solvent-free conditions, and treatment of the latter with aqueous ammonia affords amide (168) (Scheme 3.119, Eq. 1). 

Substituents such as long-chain alkyl, alkoxy, or alkylamino groups and also sulfonic acid functions tend to increase solubility. 

The photoactive compounds, or sensitizers, that are used in the formulation of positive photoresists, are substituted diazonaphthoquinones shown in Figure 17. The substituent, shown as R in Figure 17, is generally an aryl sulfonate. The nature of the substituent influences the solubility characteristics of the sensitizer molecule and also influences the absorption characteristics of the chromophor (79). The diazonaphthoquinone sulfonates are soluble in common organic solvents but are insoluble in aqueous base. Upon exposure to light, these substances undergo a series of reactions that culminate in the formation of an indene carboxylic acid as depicted in Figure 17. The photoproduct, unlike its precursor, is extremely soluble in aqueous base by virtue of the carboxylic acid functionality. 

In particular, it should be noted that since 11-deoxycorticosterone does not exhibit glucocorticoid activity yet, it is a powerful mineralocorticoid and has only two potentially reactive substituents capable of reacting with a receptor, and the interaction should occur by way of a Cj-keto and/or a Ci7j3-C0-CH20H groups. The necessity of either a simultaneous presence of acidic functions at Cu and or the necessity of simultaneous absence of acidic functions at and C17 in the structure of the pregnane system is also apparent. 

There is a means of determining the acidity site based on the extent of transmission of the electrical effect. We have shown that electrical-effect transmission in a data set is dependent on L, the coefficient of a L is a function of the number of bonds, n, intervening between the nearest atom of the substituent and the atom losing the proton. For 2 period elements in a number of acidic functional groups, the average values of L are ... 

Eq. 8-28 Data from Williams (1984). Use instead of acid function (Table 8.5). 

A CH-group, which bears vinyl and sulfide substituents, is acidic enough to be metallated by strong bases. Other d3-synthons may contain two activating functional groups in Imposition ( homoenolate -equivalents). Only one of the a-carbons is deprotonated under appropiate conditions (e.g. succinic diesters). Ano ther possibility is an acidic carbon and a non-acidic functional group in 1,3-positions (e.g. propargyl derivatives). Silyl ethers of a, -unsaturated alcohols can also be converted to anions, which react as d3-synthons (W. Oppolzer, 1976). 

Thus, the pKa values of an acid is only determined by its rate of dissociation [reaction (1)]. Hence, in a homologous series, electron-withdrawing substituents reduce the pKa value by rendering the environment of the acidic function more positive and thereby accelerating the rate of dissociation of the (positively charged) proton. In contrast, an electron-donating substituent increases the pKa value. 

The principal polyphosphazenes that have been used in hydrogels are those with linear or branched ethyleneoxy side chains, aryloxy groups with carboxylic acid substituents, or mixed-substituent polymers that bear hydrophilic methylamino side groups plus a hydrophobic cosubstituent such as phenoxy or trifluoroethoxy. Cross-linking is usually accomplished by gamma-ray irradiation or, in the case of the carboxylic acid functional species, by treatment with a di- or tri-valent cation. Here, we will consider another example based on MEEP (3.79), a polymer that is well suited to the clean method of radiation cross-linking. 

Because the anhydride is cyclic, its structural units are not incorporated into a ketone and a carboxylic acid as two separate product molecules. Rather, they become part of a four-carbon unit attached to benzene by a ketone carbonyl. The acyl substituent terminates in a carboxylic acid functional group. 

In order to form the anti-products enantioselectively, the reaction face of either the enamine or the imine must be opposite that utilized in the proline-catalyzed reactions. In the reactions catalyzed by 13 (Scheme 2.15b), the methyl group at 5-position of the pyrrolidine ring acts to fix the conformation of the enamine and the acid functionality at the 3-position controls the enamine and imine face selection in the transition state (Scheme 2.15b). In order to avoid steric interactions between the substituent at the 5-position of this catalyst and the imine in the transition state, catalyst 13 has a trans configuration for substituents at the... 

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