Carboxylate ions absorption bands

Group III (Types I, IX, XXVII, and XXXIII) showed both amide and carboxylate ion absorption bands, although these bands were poorly resolved. 

Group IV (Types VIA, VIB, XVII, XVIII, XXIII, XXVIII, and XXXII) showed neither amide nor carboxylate ion absorption bands. Absorption bands at 5.77 p were correlated with the presence in the polysaccharides of 0-acetyl functions. With few exceptions, the presence of amide and carboxylic acid groups has been confirmed by chemical evidence (see Table II). 

Bobrowski and Das33 studied the transient absorption phenomena observed in pulse radiolysis of several retinyl polyenes at submillimolar concentrations in acetone, n -hexane and 1,2-dichloroethane under conditions favourable for radical cation formation. The polyene radical cations are unreactive toward oxygen and are characterized by intense absorption with maxima at 575-635 nm. The peak of the absorption band was found to be almost independent of the functional group (aldehyde, alcohol, Schiff base ester, carboxylic acid). In acetone, the cations decay predominantly by first-order kinetics with half life times of 4-11 ps. The bimolecular rate constant for quenching of the radical cations by water, triethylamine and bromide ion in acetone are in the ranges (0.8-2) x 105, (0.3-2) x 108 and (3 — 5) x 1010 M 1 s 1, respectively. 

As Smith (300) has shown by infrared spectroscopy, carboxylic acids are adsorbed either by hydrogen bonding of the carboxyl group or by proton transfer to the surface. Carboxylate absorptions were observed in the spectra. Very likely O " or OH ions acted as proton acceptors although no OH absorption bands could be detected after carboxylic acid adsorption. The isoelectric point of pure anatase is near pH 6.6 (305). 

The conversion of a carboxylic acid to a salt can serve as confirmation of the acid structure. This is conveniently done by the addition of a tertiary aliphatic amine, such as triethylamine, to a solution of the carboxylic acid in chloroform (no reaction occurs in CC14). The carboxylate ion thus formed shows the two characteristic carbonyl absorption bands in addition to an ammonium band in the 2700-2200 cm-1 region. The O—H stretching band, of course, disappears. The spectrum of ammonium benzoate, Figure 3.24, demonstrates most of these features. 

Complexes obtained by interactions between aliphatic amines and carboxylic acids have a structure type of the ion pair and complex composition 1 1. Their IR spectra do not have the characteristic absorption band for free yC=0 in the region from 1780 to 1700cm . However, new characteristic absorption bands appear for the carboxylate anion in 1680-1560cm (uas COO ) and 1400-1300cm (y COO ). Some additive bands also appear The vibration NH" HO (in the region 2800-2200 cm ), as in the salts in solid state, and the bands NH2" or... 

NHs" " at 1620-1600cm , and C02 at 670cm (where y is stretching or valence vibration and d is deformation vibration). The complex with composition 2 1 can be formed as a result from the addition of a second acid molecule to an ion pair (in increased amine concentration). Characteristic absorption band of the carboxylate anion shifts to the lower values of the wave numbers (as compared to the complex with 1 1 composition). ... 

Some derivatives of both thiazole and benzothiazole have been studied by IR spectroscopy. In particular, an extensive study has been carried out with thiazole-2-carboxylic acids and the corresponding carboxylate ions <88Mi 306-01 >. The infrared spectra of 2,3-disubstituted 1,3-thia-zolidin-4-ones have been studied and the majority of the absorption bands assigned <93PS(78)223>. The tautomerism of thiazoles substituted in 2- and 4-position by amino, thio, and hydroxy groups was examined by infrared spectroscopy (85JPR25l> (see Section 3.06.4.4). 

In summary, the titration experiments show that the 1235 cm 1 band is unaffected by any of the neutralization processes while progressively stronger bases increase the intensity of the 1595 cm 1 region by converting the carboxylic acid functionality (1725 cm 1) to the carboxylate ion (1590 1380 cm 1). In addition, these (and other related) experiments indicate the presence of a very stable compound in these carbon blacks which is characterized by an absorption at 1700 cm 1 (aldehyde ). There is no evidence from the vibrational spectra for the phenolic and lactone functionalities seen on other carbonacous compounds. 

Group II (Types II, III, VIII, XXII, XXXI, and XXXVIII) showed absorption bands at 6.20 and 7.10 n, characteristic of the carboxylate ion. 

For phosphorescence, lanthanide metal ions can be used in a similar manner. Lanthanide ions have very interesting photophysical properties, but often exhibit weak absorption bands, and aggregate to form clusters, which limit their applications. Thus, a dendrimer that can provide a protective shell to isolate a cation and at the same time enhance the emission by transfer from the periphery to the lanthanide ion at the core could be of great interest. Self-assembled lanthanide-cored dendrimers have been prepared to prove such an assumption synthesis was carried out by mixing three equivalents of polyaryl ether dendrons bearing carboxylic acid entity at the focal point with Ln(III) cations [Er(III), Tb(III), and Eu(III)] (Fig. 5.4) [34]. The authors demonstrated that the enhancement of the lanthanide cation emission associated with the dendritic core shell was observed, and an antenna effect from the periphery to the core was shown to promote this process. 

The protonated carboxylic acid group has a strong absorption at 1,700 cm that is assigned to the C = 0 stretching mode. The bond order of the C-0 bond in carboxylate ions is less than that of the corresponding carboxylic acid. As a result, the position of the v(C = O) mode of the carboxylic ion is shifted towards lower wavenumber and appears at 1,560 cm Both absorption bands are overlaid by the 5(OH) mode of water which is located at 1,630 cm ... 

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