Molecular structure and hydrogen bonds in solid dimethylol propionic acid (DMPA)

Abstract

The H-bonds in dimethylol propionic acid (DMPA) are investigated through the spectra changes between −150 and 180 °C, the spectra comparison before and after the pendent carboxylic group was neutralized as well as after DMPA was partly deuterated. Vibrational bands assignment is proposed based on the group frequency, band shape, intensity and the crystal structure. It was found that the highly crystallized DMPA is also highly H-bonded with the obvious crystal relating bands besides the typical H-bonded characteristic bands of both alcohols and carboxylic acids. The packing mode of carboxylic acid is similar to long-chain polymers to some extent but possesses the dimer spectra characteristic, especially still showing the prominent out-of-plane bending vibrational band γOH. The three hydroxyls, including the carboxylic hydroxyl, are all in the different H-bond states, showing three H-bonded hydroxyl bands with different frequencies. The frequency, intensity and shape of νOH relates not only to OH bond length, but also to H-bond length as well as the bond angle. The H-bond in carboxylic hydroxyl is more sensitive to temperature changes and deuteration whereas the two primary hydroxyls form another H-bond pattern after DMPA was neutralized. It was also found that the possible overtone of γOH appears at lower temperature.