Infrared spectra carboxylic acid group

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). 

Fingerprint region (Section 13 20) The region 1400-625 cm of an infrared spectrum This region is less character istic of functional groups than others but varies so much from one molecule to another that it can be used to deter mine whether two substances are identical or not Fischer esterification (Sections 15 8 and 19 14) Acid cat alyzed ester formation between an alcohol and a carboxylic acid... 

The most obvious feature in the infrared spectrum of a carboxylic acid is the intense carbonyl stretching absorption. In a saturated acid, this vibration occurs around 1710 cm-1, often broadened by hydrogen bonding involving the carbonyl group. In conjugated acids, the carbonyl stretching frequency is lowered to about 1690 cm-1. 

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. 

The trans-fused octahydrobenzo[g]quinoline (60) is formed when the related 2-benzylpiperidine-3-carboxylic acid is heated in polyphosphoric acid. The 5-carbonyl group in the product is reduced to a metl lene group by lithium aluminium hydride-aluminium chloride (J.G. Cannon et dl. J. med. Chem., 1984, 190). The stereochanical assignment is based on the strong absorption at 2780 cm in the infrared spectrum of (60) and the large (65 Hz) chemical shift difference exhibited by the benzyl... 

On the other hand, the electric resistance of the membrane before the reaction with phosphorous pentachloride and triethylamine was 1,1 - cm2 and l,0i2- cm2 respectively when measured in the environment of 3,5 N sodium chloride solution to its one side and 6.0 N sodium hydroxide solution to the other side, and in the environment of 3.5 N sodium chloride solution of pH 0,5, According to reflective infrared spectrum, the absorption bands observed were different between the surfaces reacted with phosphorous pentachloride and non-reacted. Namely the absorption band at 1680cm 1 corresponding to carboxyl groups was observed, and the absorption band at 1060cm l observed in the sulfonic acid type membrane disappeared on the surface which had been reacted with phosphorous pentachloride. 

Though this is not an acid salt, and does not even involve any carboxyl groups, its structure is analogous to that of a Type A acid salt, as was predicted by Hadzi and Novak 36) from its infrared spectrum, and confirmed by X-ray work 37). 

The major baninfrared spectrum of carboxylic acids (which contain the COOH group) are summarised in Table 4.3h. ... 

Examination of the infrared spectrum for compound C indicates a strong band at 1700 cm , which denotes a carbonyl group. This functional could belong to an aldehyde, ketone, carboxylic acid, or ester. However, the strong and broad band between 2500 cm and 3000 cm , indicates a -COOH group exists. That this is an acid is also confirmed by the C-0 stretching at 1250 cm i. If the formula of compound C is C7H6O2 and COOH is accounted for, then CeHs is still to be determined. This formula fits benzene very well. 

The infrared spectrum of the product was similar to that for the starting polymer with additional peaks due to carboxylic acid and ketone carbonyl functional groups. Figure 1 shows the infrared spectra of the starting poly (IB-PMS) copolymer... 

Figure 1 shows the infrared spectra of the p-ketocarboxylic acid-functionalized poly (IB-PMS) copolymer (middle spectrum) and the ester-functionalized poly (IB-PMS) copolymer (top spectrum). The infrared spectrum of the ester product shows the disappearance of a broad peak at 3500-3100 cm" 1 due to the carboxylic add group and the appearance of new characteristic ester peaks at 1738 cm" and 1718 cm", in addition to the carbonyl peak at 1610 cm"l (Figure 1). This suggests complete conversion of the acid-fiinctionalized polymer to the ester-frmctionaliz(Kl polymer.

The most important metal-containing heat stabilizers in PVC can also be identified through IR-spectroscopy (see Section 8.2). Characteristic absorption bands for the salts of carboxylic acids are the bands of the ionized carboxy group in the region from 1590 to 1490 cm and from 1410 to 1370 cm Since the exact position of the absorption bands depends mainly on the metal counterions of the carboxy group, the IR-spectra provide a first identification of these metals. Tin stabilizers also show characteristic bands in these regions of the IR-spectrum. To determine the spectra, one uses pressed pellets made by finely grinding the sample material with potassium bromide. The identification of the metal becomes even more certain if an FT-IR (Fourier Transform/Infrared) instrument is available. With such an instrument, it is possible to subtract the spectrum of an additive-free... 

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