Infrared Absorption Spectra.Some Long-Chain Fatty Acids, Esters, and Alcohols

Abstract

Infrared absorption spectra from 2 to 15 microns are given for a number of pure long-chain saturated and monounsaturated fatty acids, methyl esters, triglycerides, and alcohols. The four classes of compounds studied are readily distinguished by spectral features common to the members of each class. Within each class, trans compounds are readily distinguished from cis and/or saturated compounds, but the two last-named types can be differentiated only by careful examination of their AS A preliminary step in the application of infrared spectros-_i\_ copy to a variety of problems being conducted in the authors' laboratories, and in particular to studies of the reaction of fatty materials with oxygen, it was necessary to obtain reference spectra from 2 to 15 microns on a wide variety of pure longchain compounds. With few exceptions (1, 21) published spectra on long-chain aliphatic compounds cover a limited range {10, 18, 20) or the purity of the starting materials is unknown {3).

Inhibition of Clostridium botulinum by p -Hydroxybenzoic Acid n -Alkyl Esters

“…The spectra of methyl, ethyl, and n-propyl p-hydroxybenzoates (19), determined in a Nujol muLL Variations were observed in the intensity ratio of the bands at 1,590 and 1,605 cm-', pertaining to the degenerate isomeric splitting (2). Characteristic absorptions at 1,670 and 1,280 cm-' were recorded, corresponding to the stretching vibrations of C=O and C-OR bonda, respectively (2,22). With increase of the ester chain the C=O frequencies tend to increase by about 10 units, and those of C-OR tend to decrease by about 5 units (Table 1).…”

Constituents of Huleh Peat. III. Acids

“…Infrared measurements of the isolated esters were carried out in sandwich cells and the spectra compared with those of standard solutions of the methyl esters of known fatty acids. The spectra showed strong absorption bands in the 3.4 -3.5p region, indicating the presence of methyl and methylene groups, a band at 13.8/.1 indicating methylene chains with four or more carbon atoms, the ester carbonyl absorption at 5.75/.1, and a triplet pattern of peaks at about 8.0, 8.3 and 8.51J which are characteristic of methyl esters of long-chain fatty acids [24].…”

Lipid analysis by vibrational spectroscopy

“…For about half a century, infrared (IR) spectroscopy has been successfully used to distinguish between isomers with cis and trans double bond configurations and to determine the total isolated (non-conjugated) trans content of fats and oils [1]. These experiments were carried out on dispersive IR instrumentation and required milligram quantities of analytes.…”

“…This progress allowed the on-line measurement of FTIR spectra for sub-nanogram-level analytes eluting from a capillary gas chromatographic column. Hence, individual compounds and isomers in complex mixtures of saturated and unsaturated fatty acid derivatives could be identified by capillary gas chromatography (GC)-FTIR spectroscopy [1,3].…”