Carboxylic acids infrared frequencies

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... 

Poly(acrylic acid) (PAA), a MIP film candidate, has been shown to bind to the bare CdSe surface from methanol solution with considerable affinity [13]. Placement of drops of a PAA-methanol solution on the surface of CdSe and evaporation of the solvent leaves a PAA film on the semiconductor surface. Once coated with this PAA film, CdSe shows no change in PL intensity in the presence of amines. Despite the lack of a PL change, the deprotonation of the carboxylic acid could be observed by the shifting of the infrared (IR) carboxylic acid peak to lower frequencies characteristic of the carboxylate anion upon amine binding, as shown in Fig. 5. The reaction chemistry is ... 

The vibrational spectrum of 4-pyridine-carboxylic acid on alumina in Fig. 4d is equivalent to an infrared or Raman spectrum and can provide a great deal of information about the structure and bonding characteristics of the molecular layer on the oxide surface. For example, the absence of the characteristic > q mode at 1680 cm 1 and the presence of the symmetric and anti-symmetric O-C-O stretching frequencies at 1380 and 1550 cm indicate that 4-pyridine-carboxylic acid loses a proton and bonds to the aluminum oxide as a carboxylate ion. 

Collette (1992) proposed a novel approach to developing and applying QSARs for the alkaline hydrolysis of carboxylic acid esters using infrared (IR) spectroscopic data. The concept is to extend QSARs to a larger and more diverse group of organic compounds by including the structural information encoded in IR spectra. Such data are available from spectral data bases, but even in the absence of literature data, IR frequencies are readily measurable. 

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. 

Gu, Z., Zambrano, R., and McDermott, A., Hydrogen bonding of carboxyl groups in solid-state amino acids and peptides Comparison of carbon chemical shielding, infrared frequencies, and structures, J. Am. Chem. Soc. 116, 6368-6372 (1994). 

Infrared studies have shown dependence of the carbonyl absorption value of a series of heteroannularly disubstituted ferrocene carboxylic acids and their methyl ethers on changes in the substituent in the other ring. Nes-meyariov and co-workers (31) have detected a shift to lower frequencies of yc=o values with increasing electron donation. For example, the carbonyl absorption was observed to be 1704 cm for I -sulfuralfluoroferrocene-carboxylic acid, but when the substituent was a methyl or ferf-butyl the... 

Carboxylic acid azides have been analysed and again, the characteristic asymmetric stretching frequency is 2140 cm . Substitution alpha to the carbonyl group has little effect d . A review of the infrared characteristics of carbamoyl azides has appeared which cites 2150 cm as the characteristic frequency for the azido group. 

An infrared study of the 2-carboxylic acids has shown that the C=0 absorption frequency is a direct function of the electron-withdrawing power of the heteroatom.61... 

Aldehydes Amides Carboxylic acid anhydrides Carboxylic acids Esters Ketones and functional groups, 56 infrared absorption frequencies, 519,... 

Extensive infrared studies have been made on metal complexes of carboxylic acids. Table 111-16 gives the infrared frequencies and band assignments for the formate and acetate ions obtained by Itoh and Bernstein. The carboxylate... 

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