The Infra-Red Absorption of Carboxylic Acids in Solution II. Intensities

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Abstract
The integral absorption of the monomeric OH band has been measured for solutions of acetic, benzoic and lauric acids in CCl4 at various concentrations and temperatures. At any given temperature the results indicate that the integrated intensity is roughly proportional to the amount of the monomer present, assuming that there is a monomer⇌dimer equilibrium. The temperature variation of the integrated absorption gave values for the heat of association varying from 6000 to 10,000 cal./g mole, which is considerably below the accepted value of 15,000 cal./g mole. This difference is attributed to the variation in the absorption coefficient with temperature. Equally anomalous results were obtained from measurements on the intensity of the monomeric C=O band. The variation of the absorption coefficient with concentration and with temperature was checked independently on solutions of cetyl alcohol in CCl4.