Complex formation of halogenated alcohols with various electron donors

The results are reported of a study, by the near i.r. spectroscopic method, of the hydrogen bonding between 2-bromoethanol, 2-chloroethanol and 2-fluoroethanol, and hexamethylphosphortriamide, dimethyl sulfoxide, dibenzyl sulfoxide, di-p-tolyl sulfoxide and diphenyl sulfoxide in carbon tetrachloride at 288.15, 298.15, 308.15 and 318.15 K.The K₁₁, ΔH°, ΔG° and ΔS° values for the complex formation show that the complex formation ability of the 2-halogen substituted ethanols is weak towards the selected electron donors and much weaker than found earlier for the corresponding 2,2,2-trihalogen substituted ethanols. The basicity order of the electron donors decreases in the order hexamethylphosphortriamide ⪢ dimethyl sulfoxide ⪢ dibenzyl sulfoxide ⪢ di-p-tolyl sulfoxide ⪢ diphenyl sulfoxide, while the proton donating ability of the halogenated alcohols is in the order 2-bromoethanol ⪢ 2-chloroethanol ⪢ 2-fluoroethanol. The pK_a values of the alcohols determined in water are in the same order. Therefore the order of the complex formation ability is opposite to the acidity order in water.