Acid halides infrared spectroscopy

D.E.H. Jones and J.L. Wood (ref. 7) used infrared spectroscopy to study the chloride complexes of acidic A1C13. The study of the complexation of acetyl chloride by the various metal halides (Table 1) was performed by measuring the variation of the vibration intensity (CO) at 1808 cm. ... 

In many instances, however, it is possible to purify imidoyl halides by vacuum distillation. If the compounds are thermally sensitive, purification can be conducted by solution in nonpolar organic solvents, in which the polar by-products, as well as products formed by self-condensation, are less soluble, or completely insoluble. While it is often difficult to establish melting points, because recrystallization and thereby exposure to moisture results in partial conversion to the corresponding carboxylic acid amides, identification by infrared spectroscopy is a good analytical tool. The characteristic spectral feature of the imidoyl halides is the C=N double bond absorption which occurs at 1650-1689 cm in imidoyl chlorides (see Table V). 

Acid Halides and Anhydrides Acid halides and anhydrides are rarely isolated as unknown compounds but they are commonly used as reagents and intermediates, and PROBLEM-SOLVING infrared spectroscopy can confirm that an acid has becai converted to a pure acid chlo-... 

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. 

ECD = electron capture detector EPA = Environmental Protection Agency FEWS = fiber evanescent wave spectroscopy FID = flame ionization detection FT-IR = Fourier transform infrared GC = gas chromatography HECD = Hall electrolytic conductivity detector HRGC = high resolution gas chromatography HSD = halide-sensitive detector H2SO4 = sulfuric acid LDPE = low-density polyethylene MS = mass spectrometry NIOSH = National Institute for Occupational Safety and Health NR = not reported PI = photoionization UV = ultraviolet detection... 

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