Effect of surface adsorption on the determination by infrared spectroscopy of hydrogen bond energies in carboxylic acid dimers

Abstract

The enthalpies of dimerization of formic, acetic, and propionic acids have been measured in the gaseous state. Repeated determinations with different surface areas resulted in marked changes in apparent enthalpies. Gross discrepancies in literature values are resolved when corrections for surface adsorption are made. All dimers of carboxylic acids that have been studied in the gas phase have bonds of equal strength when results are corrected for adsorption. The average of all appropriate values, including this study, yields an average hydrogen bond energy at 300°k of 6·8 ± 0·2 kcal./mole.