SPECTROSCOPIC STUDIES OF ALCOHOLS: II. THE CONFORMATION OF 2-HALOETHANOLS IN CARBON TETRACHLORIDE SOLUTION

Abstract

Of the five conformers predicted for 2-haloethanols, only two (halogen and OH trans and gauche) can be positively identified by high resolution infrared spectroscopy. From the temperature dependence of the relative intensities of the fundamental OH stretching bands of the trans and gauche forms of the compounds XCH2CH2OH2 where X = F, Cl, Br, and I, the gauche conformers are shown to be energetically favored in dilute carbon tetrachloride solution, with enthalpy differences between the two conformers of 2.07 ± 0.53, 1.20 ± 0.09, 1.25 ± 0.08, and 0.81 ± 0.09 kcal/mole respectively. Equilibrium constants and the conformational free energy and entropy differences are reported. Inter- and intra-molecular OH … X hydrogen-bond interactions are found to be similar in that the enthalpy increases in the order X = I < Br < Cl < F, and is linearly related to a decrease in the fundamental OH band shift, in contrast to the Badger–Bauer relationship. The molecular and thermodynamic factors governing conformational equilibria involving intramolecular hydrogen bonds are discussed.