The relative intensities of the C-X stretching bands of the gauche and trans isomers in the vapor were ineasured 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 i 0.1 kcal mole-' respectively for the two halogenated ethanols. Similar measurements on the 0-H stretching bands gave values higher than the above by 0.45 kcal mole-' 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 CICH,-.CH,OD has led to unambiguous assignment of the OH bending and torsional frequencies. The spectra of the solid show that 2-chloroethanol can exist in t u o different crystalline phases: a stable one consisting of gauche n~olecules only, and a metastable one containing both isomers.L'intensite relative des bandes de valence C-X dans le spectre infrarouge de la vapeur a ete mesurte en fonction de la tenlperat~~re jusqu'a 165 'C pour le 2-chloroethanol et jusqu'a 130 "C pour le 2-bromoethanol. De ces mesures on tire les valeurs 1.20 et 1.45 ? 0.1 kcal mole-' respectivement pour les differences d'enthalpie entre les isomeres gauche et trans. Par contre des mesures senlblables faites sur les bandes de valence 0-H conduisent a des valeurs de AHplus elevees d'environ 0.45 kcal mole-' pour les deux composCs. Ce desaccord est probablement dil a la presence d'un troisieme isomere, de configuration gauche, mais sans liaison hydrogene intramoleculaire.Une e t~~d e de la nlolCcule isotopique C1CH2-CH,OD a permis d'identifier sans ambiguitk les bandes de deforination OH. Les spectres du 2-chloroethanol a l'etat solide ont revel6 deux ~h a s e s cristallines distinctes: I'une stable, neecontenant que l'isomere gauche, I'autre metastable, faite d'un melange des deux isomeres.
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