Side groups benzoic acid

Mesomorphic order in polymers with side groups containing the cholesterol moiety has scarcely been studied in spite of the importance of cholesterol derivatives in the field of liquid crystals and biological materials. The main focus of attention has been 

A recent publication (13) which appeared while this work was in progress described the spontaneous development of layered order in polymers with the cholesteric moiety attached to the backbone via a long, flexible molecular spacer constituted by an Co-amino-carboxylic acid chain. Layered structures are developed with the long side groups roughly perpendicular to the main chain. The authors attributed the development of these structures to the flexibility of the bridge connecting the cholesterol moiety. 

Monomers. Cholesteryl p-acryloyloxybenzoate (ChAB) was prepared in three steps by the following synthetic route  

The product was recrystallized from chloroform/acetone and chloroform/ethanol to constant transition temperature. Elemental analysis Calcd. for C3 7Hr O C, 79.29% H, 9.29%. Found C, 79.51% H, 9.3I%7 The NMR spectra were consistent with the expected structure.  

Cholesterylmethacrylate (ChMA) was obtained by a procedure similar to the one described in the literature (15 ).  

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The liquid crystalline side chain polymers investigated have either a polysiloxane (compounds SiCl and SIGN) or a polyacrylic (compound AcCN) polymer chain. These are coupled via flexible spacers with the mesogenic p-substituted benzoic acid phenylester groups. SiCl and SiCN are copolymers with p-methoxy components in excess. 

Hammen equation A correlation between the structure and reactivity in the side chain derivatives of aromatic compounds. Its derivation follows from many comparisons between rate constants for various reactions and the equilibrium constants for other reactions, or other functions of molecules which can be measured (e g. the i.r. carbonyl group stretching frequency). For example the dissociation constants of a series of para substituted (O2N —, MeO —, Cl —, etc.) benzoic acids correlate with the rate constant k for the alkaline hydrolysis of para substituted benzyl chlorides. If log Kq is plotted against log k, the data fall on a straight line. Similar results are obtained for meta substituted derivatives but not for orthosubstituted derivatives. 

In para-amino benzoic acid, there is another resonance structure right next to the six-sided ring. It is a carboxyl group, shown with a single bond between carbons, and a double bond between the carbon and the oxygen. This is also a place where the electron can bounce around between the three nuclei. 

Replacement of the hydroxyl group on the phenyl ring with a carboxyl group forms a molecule of benzoic acid. Addition of a hydroxyl at the 2-position on a benzoic acid molecule forms 2-hydroxybenzoic acid or salicylic acid. The slightly more complex phenylpropanoid skeleton contains a linear three-carbon chain (the propanoic group) added to the benzene ring (the phenyl group). Addition of ammonia to carbon 2 of this three-carbon side chain yields the amino acid phenylalanine (Fig. 3.3). Phenylalanine... 

As can be expected, the high-temperature processing runs the risk of enhancing side and consecutive reactions. Decarboxylation of the main product was found and increases with temperature (see Fig. 7). This is illustrated at the example of the synthesis of 2,4,6-trihydroxy benzoic acid from phloroglucinol, as this molecule is even more sensitive to thermal destruction due to the enhanced electron richness of the aromatic core by presence of a third hydroxyl group (Hessel et al. 2007). 

The oxidation of dihetarylethene 44 with m-chloroper-benzoic acid (m-CPBA) in CH2CI2 afforded 1,1-dioxide 67 (06T5855, 073173, 08CC4622, 09JMC97) in yields up to 90% in the case of the 6-acetyl derivative, the yield of bis-sulfone 68 was only 35% (06T5855) because of a Baeyer-ViUiger oxidation side reaction of the carbonyl group. Protection of the latter as the dioxolane derivative made it possible to increase the yield of 69 to 72% (Scheme 21). 

Compound retention during RP-HPLC depends on the relative hydrophobicity of the sample compounds. As expected, the elution of phenolics for reversed-phase HPLC is in the order of decreasing polarity. Polarity is increased most by hydroxyls at the 4-position, followed by those at the 2- and 3-positions. Availability of the methoxy group and the acrylic substitution reduces polarity and increases retention times (4). Loss of polar hydroxy groups and/or addition of methoxy groups can decrease the polarity within each class of benzoic and cinnamic acid. Also, the presence of the ethylenic side chain in the cinnamic acids can reduce their polarity compared with similarly substituted benzoic acids (6). The elution order for benzoic acids is as follows (Table 1) gallic > a-resorcylic > protocatechuic > y-resorcylic > gentisic > p-hydroxyben-... 

Some support for this mechanism derives from our observation of benzyl radical from phenylacetic acid, phenoxymethyl radical from phenoxy-acetic acid, and possibly the phenyl radical from benzoic acid. Radical spectra were not found for several aryl acids with longer side chains but this is not inconsistent because the 0-phenylethyl and higher radicals are not expected to absorb strongly above 300 m/z. The case of the heterocyclics is complicated by the possibility of excitation either via the 7r-system or a lone pair electron on the heteroatom, and discussion of this group will be deferred until additional experimental data are obtained. 

The second impetus to consider monomers with dendritic side groups comes from the work of Percec et al. on monomers with tapered side chains, e.g., polymerization of 3,4,5-tris (4 -dodecyloxybenzyloxy) benzoic acid ethylene glycol (n=l,2,3,4) methacrylates... 

Side chains of alkylbenzenes are oxidized to benzoic acid derivatives by treatment with hot potassium permanganate or hot chromic acid. Because this oxidation requires severe conditions, it is useful only for making benzoic acid derivatives with no oxidizable functional groups. Oxidation-resistant functional groups such as —Cl, —NO2, —SO3H, and —COOH may be present (Section 17-15A). 

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