Identification of fatty acid polymorphic modifications by infrared spectroscopy

Abstract IR spectra in the 7.5–25.0 μ region are shown to be unique for the individual long chain odd carbon numbered saturated fatty acids and for the monounsaturated even carbon numbered fatty acids, their isomers, and polymorphic modifications. IR spectra are presented which illustrate similarites and dissimilarities resulting from chain length differences and polymorphic variations for monounsaturated acids. X‐ray crystal long spacings for the saturated odd carbon numbered acids are compared with literature values. X‐ray crystal long spacings for monounsaturated trans acids are shown to be related to carbon chain length and independent of the location of unsaturation. Diffractograms and IR spectra of the 2 polymorphic modifications of elaidic acids are presented. IR spectra illustrating band differences for cis and trans isomers are shown.