Infrared quantification of ethanol and 1-butanol hydrogen bonded hydroxyl distributions in cyclohexane

Quantifying the mid-range infrared hydroxyl stretch absorbance region has traditionally been a challenge due to the wavenumber dependence of the attenuation coefficient. Interpretation often assigns a single attenuation coefficient to each type of hydrogen-bonded aggregate. This work leverages a recently developed technique of scaling hydroxyl stretching absorbances in the mid-infrared region with a continuous attenuation coefficient function that produces integrated areas which directly correlate to hydroxyl concentrations. After scaling, the hydroxyl absorbance is fitted with five curves, of which four are dominant. These four curves represent unique hydroxyl configurations and translate to specific aggregate structures. The technique is applied to ethanol and 1butanol. The resulting population distributions of hydrogen-bonded hydroxyl configurations are compared with the resummed thermodynamic perturbation theory (RTPT) model for linear chains as a function of concentration and temperature. The model is demonstrated to capture the critical features of the distributions.

Automated summary

This study presents a new approach to quantify the mid-range infrared hydroxyl stretch absorbance region using a continuous attenuation coefficient function. The results show that the technique can provide integrated areas directly correlated to hydroxyl concentrations and determine unique hydroxyl configurations. The comparison with the thermodynamic perturbation theory model demonstrates the accuracy of the method in capturing the distribution features of hydrogen-bonded hydroxyl configurations.