Carboxylic acids, conjugated liquids

The polarity and polarizability of the central groups of mesogenic compounds are more clearly correlated with thermal stability. Thus, 4-alkoxy-4 -biphenyl carboxylic acids, form more stable mesophases than corresponding 4-alkoxybenzoic acids. Similarly, esters of cholesterol form generally more thermally stable mesophases than esters of cholestanol. These differ only by the presence of a double bond, as shown in Fig. 5. Again, certain conjugated unsaturated aliphatic carboxylic acids show liquid crystalline phases, while normal aliphatic... 

For applied purposes, the book by Mitskevich and Erofeev [31] is of interest because it discusses conjugated reactions on the example of decarboxylation processes accompanying the liquid-phase oxidation of carboxylic acids. 

The most important characteristics of the Rhodonines are not their hormonal properties, as in the case of the retinenes, but their electronic properties, especially when in the liquid crystalline state. These properties are not directly relatable to their relatives, the retinenes. They are more closely associated with another group of relatives, the oxonols. The oxonols consist of two oxygen atoms connected by a conjugated carbon chain. The oxonols and the phthaleins are members of the carboxylic acid family, a large well-known family of dyes. ... 

Neither of these compounds is very soluble in water, but both dissolve in a less polar solvent such as dichloromethane (CH2C12). If this solution is extracted with aqueous sodium hydroxide, the benzoic acid reacts to form a salt that is soluble in the aqueous phase. Therefore, when the two liquids are separated the carboxylic acid salt is in the aqueous phase and the naphthalene remains in the dichloromethane. The compounds have now been separated. To recover the carboxylic acid it is necessary to protonate its conjugate base. This can be accomplished by treating the aqueous solution with a strong acid such as hydrochloric acid. The equilibrium shown in the following equation favors the weaker acid the carboxylic acid which then precipitates from the solution ... 

Enantiomers can be separated by high-performance liquid chromatography in which the column material, or matrix, is covalently bonded to a chiral ligand. In this case, the chiral ligand is (5)-aspartic acid, an inexpensive, readily available amino acid. At pH 7, the carboxylic acid group of aspartic acid exists as its conjugate base, a carboxylate anion. The amino group is bonded to the column matrix. 

The carbonyl stretching absorption, which occurs at about 1730 to 1700 cm for the dimer, is usually broader and more intense than that present in an aldehyde or a ketone. For most adds, when the acid is diluted with a solvent, the C=0 absorption appears between 1760 and 1730 cm for the monomer. However, the monomer is not often seen experimentally since it is usually easier to run the spectrum as a neat liquid. Under these conditions, as well as in a potassium bromide pellet or a Nujol mull, the dimer exists. It should be noted that some acids exist as dimers even at high dilution. Conjugation with a C=C or aryl group usually shifts the absorption band to a lower frequaicy, as predicted in Section 2.14A and as shown in the spectrum of benzoic acid (Fig. 2.46). Halogenadon on the cr carbon leads to an increase in the C=0 frequency. Section 2.18 discusses salts of carboxylic adds. 

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