The infrared spectra of a number of conjugated unsaturated aliphatic monocarboxylic acids in the 750–250 cm−1 region are reported. Two correlation frequency ranges are reported and one of these is useful for distinguishing these compounds from other acids. In addition, the band intensities in this region may be useful for characterizing conjugated acids.
W. R. Feairheller and J. E. Katon, "Infrared Spectra-Structure Correlations of Conjugated Unsaturated Aliphatic Monocarboxylic Acids in the 750–250 cm−1 Region," Appl. Spectrosc. 22, 488-490 (1968)