Carboxylic acid derivatives infrared spectroscopy

Infrared IR spectroscopy is quite useful in identifying carboxylic acid derivatives The, carbonyl stretching vibration is very strong and its position is sensitive to the nature of IKT the carbonyl group In general electron donation from the substituent decreases the double bond character of the bond between carbon and oxygen and decreases the stretch mg frequency Two distinct absorptions are observed for the symmetric and antisym metric stretching vibrations of the anhydride function... 

Different types of carbonyl groups give characteristic strong absorptions at different positions in the infrared spectrum. As a result, infrared spectroscopy is often the best method to detect and differentiate these carboxylic acid derivatives. Table 21-3 summarizes the characteristic IR absorptions of carbonyl functional groups. As in Chapter 12, we are using about 1710 cm-1 for simple ketones and acids as a standard for comparison. Appendix 2 gives a more complete table of characteristic IR frequencies. 

Infrared spectroscopy can also be used to probe resonance in carboxylic acid derivatives. The dipolar resonance structure weakens the C=0 bond and causes a corresponding decrease in the carbonyl stretching frequency (Table 20-2). The IR data for carboxylic acids reported in Section 19-3 refer to the common dimeric form, in which hydrogen bonding reduces the stretching frequencies of both the 0-H and C=0 bonds to about 3000 and 1700 cm respectively. A special technique—vapor deposition at very low temperature—allows the IR spectra of carboxylic acid monomers to be measured, for direct comparison with the spectra of carboxylic acid derivatives. Monomeric acetic acid displays vc=o at 1780 cm similar to the value for carboxylic anhydrides, higher than that for esters, and lower than that of halides, consistent with the degree of resonance delocalization in carboxylic acids. 

Transition metal coordination of Cu(II) carboxylate groups and pyridine groups was employed as a means of coupling a telechelic butadiene-base polymer with a randomly functionalized styrenic polymer. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) indicated partial miscibility of the two polymers and Fourier transform infrared (FTIR) spectroscopy demonstrated that interactions occurred on a molecular level. When compared with blends of PSVP and the free acid derivative of CTB, the compositions based on the transition metal complex had improved dimensional stability at elevated temperatures, though there remains some question as to the stability of the copper salt to hydrolysis. Electron spin resonance (ESR) spectroscopy showed that only the... 

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). 

The combination of polystyrene-bound triphenylphosphine and carbon tetrachloride has been used for the condensation of N-alkoxycarbonyl a-amino acids and primary amines, including amino acid esters, in the presence of N-methyl-morpholine as base and refluxing dichloromethane as solvent [56]. In this case, supported triphenylphosphane oxide was isolated by filtration after the coupling reaction. The nature of the intermediate involved in the condensation was supposed to be the acid chloride, as these derivatives are found when heating polystyrene-supported dichlorotriphenylphosphorane with carboxylic acids [57, 58], However, evidence supported by infrared spectroscopy suggests the formation of... 

IR Spectra Infrared spectroscopy is of considerable importance in identifying carboxylic acids and their derivatives. The C = 0 stretching band is one of the most prominent in their IR spectra since it is always a strong band. Figure 17.2 gives the location of this band for most acyl compounds. 

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