Carboxylate infrared absorption

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

Infrared Spectra of Ionomers. Infrared absorption data, first pubHshed in 1964 (11), show that partial neutralization of ethylene—methacryhc acid introduced new absorption bands at 1480 1670 cm for the ionized carboxylate group while the 1698 — cm band of the free acid carboxyl diminishes in size (21). In addition to providing information on stmctural features, the numerous absorption bands ate significant in apphcations technology, providing rapid warmup of film and sheet under infrared radiation. 

Arachidic acid monolayers were prepared from a benzene solution on the water subphase of pH5.8(pure water) and 12.6(adjusted by addition of NaOH) at Tsp of 303 K below Tm(=328 K) of the monolayer [31]. The ionic dissociation state of hydrophilic group was estimated on the basis of the stretching vibrations of carbonyl and carboxylate groups by Fourier transform-infrared attenuated total reflection, FT-IR ATR measurements. 70 arachidic acid monolayers were transferred on germanium ATR prism, resulting in the formation of the multi-layered film. Transfer on the prism was carried out at surface pressures of 25 or 28 mN-nr1. Infrared absorption measurements revealed that almost carboxylic groups of arachidic acid molecules did not dissociate on the water subphase of pH5.8, whereas all carboxylic groups dissociated as carboxylate ions on the water subphase of pH 12.6. 

The teichoic acid shows an infrared absorption band at 1751 cm.-1, characteristic of carboxylic ester groups, which is not observed in samples from which the D-alanine residues have been removed. Removal of the u-alanine was readily effected with ammonia or hydroxylamine, when D-alaninamide or D-alanine hydroxamate were formed. The kinetics of the reaction with hydroxylamine reveal the high reactivity of its D-alanine ester linkages, which, like those in most other teichoic acids, are activated by the presence of a neighboring phosphate group. That the D-alanine residue is attached directly to the ribitol residues, instead of to the d-glucosyl substituents, was also shown by oxidation with periodate under controlled conditions of pH, when it was found that the D-alanine residues protect the ribitol residues from oxidation. Under the same conditions, all of the ribitol residues were oxidized in a sample of teichoic acid from which the D-alanine had been removed, and it is concluded that the ester groups are attached to C-2 or C-3 of the ribitol residues. 

The use of nitrogen dioxide for the selective oxidation of polysaccharides to polyuronic acids was introduced by Kenyon and his coworkers13,63 in 1941. By this means extensive oxidation of the primary alcohol groups in cellulose was obtained, through the mechanism of preferential nitration followed by decomposition of the nitric acid ester with carboxyl forma-tion.68(0< > Apparently some undissociated nitration products also were formed, since infrared absorption studies54 indicated the presence of nitrate radicals in the polyuronic acid. Side reactions produced carboxyl,... 

The presence of a carboxylic acid group is indicated by strong infrared absorption in the region of 1720 cm-1 (C=0 str.) and broad absorption between 3400 cm-1 and 2500 cm-1 (OH str.) in the nuclear magnetic resonance spectrum the acidic hydrogen (replaceable by D20) will appear at very low field (3 10-13). 

There is the 3 methods for preparing of 8-azaspiro(4.5)decane-7,9-dione, 8-(4-(4-(2-pyrimidinyl)-l-piperazinyl)butyl) monohydrochloride (U.S. Patent 3,717,634). One of them is follows a mixture of 0.1 mole of the substituted glutaric anhydride, 0.1 mole of l-(4-aminobutyl)-4-(2-pyrimidinyl)piperazine (U.S. Pat. 3,398151), and 300 ml of pyridine was refluxed until imide formation was completed. The degree of reaction was readily followed by taking an aliquot portion of the reaction mixture, removing the solvent, and obtaining the infrared absorption spectrum of the residue. When reaction is complete, the spectrum exhibited typical infrared imide bands at 1701 and 1710 cm-1 whereas if incomplete, the infrared spectrum contains amide and carboxyl absorption bands at 1680, 1760 and 3300 cm 1. 

Figure 9 shows a comparison of the infrared absorption and VCD spectra of (L-Ala), n = 3 - 5. The spectra are normalized for equal absorption intensity at 1595 cm 1, which is the frequency of the carboxylate anion antisymmetric stretching mode. The data show that the amide I intensity increases roughly linearly with the number of peptide linkages in the molecule, and that the VCD intensity increases similarly. However, the positions of the infrared absorption maxima are shifted from about 1654 cm 1 in the trimer to 1648 cm 1 in the pentamer. Similarly, the VCD zero crossing in the trimer occurs at 10 cm 1 higher frequency than in the tetramer and pentamer. We have interpreted these results [48] in terms of different solution conformations of the peptides the trimer seems to be stabilized by zwitterionic interactions, as discussed before, whereas formation of extended helices seems to occur at the level of the tetramer. 

Fig. 1. (a) A chemical structure of a 2.5th generation carboxylic acid-terminated poly(amido amine) (PAMAM) dendrimer. (b) Transmission surface enhanced infrared absorption spectra (SEIRAS) of dendrimer adlayers prepared at 30 min adsorption from aqueous solutions (0.01 wt.%) of a dendrimer at different pHs. Numerical values are pHs of the solutions, (c) Adsorption-desorption profiles as a function of time at different pHs and adlayer thicknesses at adsorption and desorption equilibrium as a function of pH for aqueous solutions (0.1 wt.%) of the dendrimer. The symbols, j and J, in the top figure denote start of adsorption and desorption, respectively. In the bottom figure, filled circle and opened square denote adlayer thicknesses at adsorption and desorption equilibrium, respectively. The dark tie denotes the calculated dendrimer size width. A solid curve is drawn to be visual, (d) Schematic illustration of dendrimers adsorbed at different pHs. Reprinted with permission from Ref. [69], 2006, American Scientific Publishers. 

FIGURE 10.2 Expanded infrared absorption spectra in the carboxylate region obtained for benzoic acid (long-dashed trace), the stoichiometric 1 1 benzylammonium benzoate salt (short-dashed), and the 1 1 cocrystal formed between benzoic acid and benzyl-ammonium benzoate (solid trace) [28]. 

The aliphatic members of the amino acids exhibit no absorption in the ultraviolet region above 220 nm, while the aromatic amino acids, HIS, PHE, TRY and TYR, show characteristic maxima above 250 nm. The zwitteronic character of the a-amino acids shows up clearly in their infrared spectra. No absorption due to the normal NH stretching frequency at 3300-3500 cm" is observed, indicating the absence of an NH2 group. Instead, a few of the peaks near 3070 cm", 1600 cm", 1500 cm" due to the NHJ are seen (except in PRO, the NHJ group absorbing at 2900 cm" ). The carbonyl absorption of the unionized carboxyl group at 1700-1750 cm" is likewise replaced by carboxylate ion absorption at 1560-1600 cm" [6]. 

These copper(II) ternary complexes are generally green-blue solids, stable in air, and fairly soluble in water, methanol, and ethanol. Furthermore, those with dicarboxylates and amino acid residues exhibit a characteristic, strong infrared absorption band around 1600 cm"1 due to the coordinated carboxylate group. The infrared spectra from 4000-200 cm 1 as well as the electronic spectra of these complexes have been recorded and assignments made.5 6... 

Infrared absorption spectral data for several oxazole derivatives,86 90 including alkyl-98 186 and aryl-263 264 substituted oxazoles, 2-amino- and substituted-amino derivatives109 112 136, 5-amino179 198-201 and 5-alkoxy-oxazoles,66 carboxylic acids,112 147 esters,126 179 184 carboxamides,199 200 4-acetyloxazoles,147 halogenoalkyl oxazoles,91 oxazolines,262 and benzoxazoles262 have been reported. 

Ludwig. This compound has an empirical formula corresponding to structure (1) and shows the ultraviolet and infrared" absorptions of a pyrrole-3-carboxylic ester. Its acetylation gives a tetra-O-acetyl derivative." Oxidation with lead tetraacetate yields ethyl 5-formyl-2-methyl-pyrrole-3-carboxylate (4), identical with the compound prepared in a different way. Oxidation with potassium permanganate in alkaline solution at low temperature yields 3-(ethoxycarbonyl)-2-methylpyrrole-5-carboxylic acid (7) which can be transformed " into the diethyl ester (8), identical... 

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