Infrared studies on rotational isomerism. III. 2-Chloro- and 2-bromo-ethanol

Abstract

The relative intensities of the C—X stretching bands of the gauche and trans isomers in the vapor were measured as a function of temperature up to 165 °C for 2-chloroethanol, and up to 130 °C for 2-bromoethanol. From these the enthalpy differences between the two isomers were found to be 1.20 and 1.45 ± 0.1 kcal mole−1 respectively for the two halogenated ethanols. Similar measurements on the O—H stretching bands gave values higher than the above by 0.45 kcal mole−1 for both compounds. This apparent discrepancy is interpreted as due to a second gauche isomer, the OH group of which is not engaged in intramolecular hydrogen bonding, and which is less stable than the trans isomer.A study of the isotopic molecule ClCH2—CH2OD has led to unambiguous assignment of the OH bending and torsional frequencies. The spectra of the solid show that 2-chloroethanol can exist in two different crystalline phases: a stable one consisting of gauche molecules only, and a metastable one containing both isomers.