Vibration Spectra and Molecular Structure IX. Further Studies of the Vapors of the Fatty Acid Series

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Abstract
The monomer spectra of the vapors of C3H7COOH, C3H7COOD and C4H9COOH have been obtained in the near infra‐red with a rocksalt spectrometer. The association of each of the following molecules: HCOOH, HCOOD and C3H7COOD has been studied in the vapor phase by measuring the variation with temperature and pressure of the intensity of some association band. The bond strengths obtained for these fatty acids are 6.2, 6.4 and 6.9 kcal. per mole per bond, respectively. The fact that the bond strengths for light and heavy formic acids agree within the experimental error although the determinations were carried out with different bands is further evidence that the spectroscopic method is satisfactory. The lower value obtained for the bond strength in formic acid by this method compared to the vapor density value is discussed. In addition, it is suggested from the experimental data available at the present time, that it does not seem possible to claim the existence of a simple linear relationship between the bond strength and Δv/v. Some results concerning v(CH) absorption in the first five members of the fatty acid series are given.