SPECTROSCOPIC STUDIES OF ALCOHOLS: V. INTRAMOLECULAR HYDROGEN BONDS IN 2-CYANOETHANOL AND IN SOME NITROALCOHOLS

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Abstract
The enthalpy difference between the trans and the intramolecularly hydrogen bonded gauche conformation of 2-cyanoethanol in dilute CCl4 solution is shown to be −0.14 ± 0.03 kcal/mole from the temperature dependence of the fundamental OH stretching bands. At higher concentrations cyclic dimers with double OH … O bonds form. The enthalpy change on dimerization is −6.1 ± 0.3 kcal/mole. A small percentage of dimers with acylic OH … O bonds are also present, but these are thermodynamically less stable than the cyclic dimers.Intramolecular hydrogen bonds are found between OH and NO2 groups in some 2-nitro-alcohols, leading to stabilization of the gauche form with respect to the trans form. For 2-nitroethanol the trans conformer is in equilibrium with two intramolecularly hydrogen bonded conformers (ΔH = −0.40 ± 0.10 and −0.71 ± 0.09 kcal/mole respectively). 2,2-Dinitro-propanol and 2-methyl-2-nitro-1,3-propanediol show complex νOH bands due to trans and intramolecularly hydrogen bonded gauche conformers. 2,2,2-Trinitroethanol has a relatively narrow symmetrical OH peak at temperatures up to 55 °C which is assigned to the exclusively populated intramolecularly hydrogen bonded conformation.