Association of water and small monocarboxylic acids: matrix isolation FTIR spectrometry study

Infrared spectra of matrix isolated formic, acetic, propionic, and butyric acids mixed with water were obtained. Combining experimental data and theoretical calculations we were able to assign spectral bands arising due to formation of 1:1 complex between water and title acids. The structure of such complexes was elucidated from theoretical and spectral data for the first time. Alternating decrease of binding energy of the complexes was observed with the increase of the length of radical chain of organic acids. Alternating behaviour of hydrogen bond energy might be attributed to the weak van der Waals interaction between oxygen atom from carbonyl group and nearest hydrogen atoms from aliphatic chain of the acid.