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

Self Cite

The i.r. spectra of 2-nitroethanol in the three physical states were measured between 4000 and 250 cm-'. The liquid and the crystal werealso studied in Raman effect. In all three states the molecules exist as gauche and trans isomers, the former being stabilized by a weak intramolecular hydrogen bond. Definite evidence for a third isomer, previously reported in dilute CCl, solutions, could not be ascertained from the vapor spectra as a function of temperature. On the other hand this study revealed appreciable decomposition of the vapor above 80 "C, with formation of nitroethylene and also some aldehyde. For that reason it was not possible to evaluate the enthalpy of isomerization. The difficulty of securing a pure sample of 2-nitroethanol is emphasized. Only one crystalline phase was obtained.On a Btudik en i.r. entre 4000 et 250 cm-l le nitro-2 ethanol sous les trois Ctats physiques. En outre on a etudie en Raman le liquide et le cristal. Dans les trois etats les ~nolecules existent sous forme d'isomeres trans et gauche. Ce dernier est stabilise par une faible liaison hydrogene interne. La presence d'un troisieme isomere, prksumement gauche, signalee dans les solutions dilutes en solvant inerte, n'a pu Ctre confirmke par une etude de la vapeur en fonction de la temperature. Celle-ci, par contre, a revel6 une decomposition appreciable a partir de 80 "C avec formation de nitrokthylene et d'un peu d'aldkhyde. Pour cette raison il n'a pas kt6 possible d'evaluer l'enthalpie d'isomkrisation gauche-trans. On souligne la difficulte de preparer un kchantillon pur de ce nitroalcool. Une seule phase cristalline a kt6 obtenue.

Section: Vapor Spectrasupporting

confidence: 62%

“…spectrum of the liquid; at least not in the early stages. The spectroscopic samples were prepared as reported previously (11,12). For the vapor spectra, because of the low volatility of the compound a 10 m folded-path absorption cell with cesium bromide windows (8) had to be used in a static system.…”

Section: Methodsmentioning

confidence: 99%

Infrared Studies on Rotational Isomerism. V. 2-Nitroethanol

Giguère¹,

Kawamura²

1971

Self Cite

“…It could be kept in that condition for a few weeks if stored in the cool, in a dark flask under nitrogen atmosphere. Because of its low volatility, of the order of 0.1 Torr at rooni teniperature, a 10 ni n~ultiple reflection cell heated electrically was used, as described previously (5). The liquid sample kept at 50 "C in a side Aask was entrained in a current of dry nitrogen.…”

Section: Methodsmentioning

confidence: 99%

Infrared studies on rotational isomerism. IV. 2-Cyanoethanol

Schneider¹,

Giguère²

1969

Self Cite

From the infrared spectra of the vapor measured between 4000 and 200 cm-', 2-cyanoethanol was found to exist as garrche and trnns isomers in roughly equal proportions around 100 "C. The gartclle form is the more stable of the two, as in 2-chloro-and 2-bromo-ethanol, but the enthalpy difference is less than half as large; at most 0.7 kcal mole-'. This indicates some weak (about 1 kcal mole-') intramolecular hydrogen bonding between the O H group and the 71 electrons of the C=N bond.In the solid, two distinct crystalline phases have been observed. Crystal 11, consisting of gauche molecules only, is normally obtained; for instance by annealing the vitreous solid froni low teniperature deposition of the vapor. Crystal I, which contains the two ison~ers, may be obtained irreversibly froni the melt of crystal I1 under controlled conditions.On the other hand there was no indication in the spectra of a cyclic tautomer as suggested recently.Les spectres infrarouges de la vapeur pris entre 60 et 140 "C ont confirm6 la presence dans le 2-cyanoethanol (CN-CH2-CH2-OH) de deux isonieres de rotation, le garrche et le trmis, en proportions a peu pres egales. L'isomere garrche est le plus stable des deux, comme dans le 2-chloro-et le 2-bromoethanol; cependant la difference d'enthalpie est moins de la moiti6 de ceux-ci, soit 0.7 kcal mole-' tout au plus. Ceci doit Ctre attribui a une liaison hydrogene intramoleculaire faible (environ 1 kcal mole-') entre le groupe OH et les electrons n de la liaison C k N .Tout commele 2-chloroethanol, le 2-cyanoCthano1 peut exister sous deux phases cristallines distinctes. La phase normale (11) faite de molCcules galrcl~es seulement, peut se transformer par fusion menagte en line phase metastable (I) qui contient les deux isomeres.Par ailleurs on ne trouve dans les spectres aucune indication d'une forme tautomere cyclique telle que proposee rCceniment .

“…absorption bands are rotational isomerism in 2-haloethanols given in Table 1, which also includes the probable was investigated by previous workers (1)(2)(3)(4), but assignments of the vibrational frequencies of the complete assignments of their vibrational frequencies were recently made by Buckley et al Discussion (5). The molecule of 2-mercaptoethanol is similar to that of 2-haloethanols, so it is expected to As the Raman spectrum of 2-mercaptoethanol show rotational isomerism, which, however, has in the crystalline state could not be obtained as not yet been reported.…”

Section: Introductionmentioning

confidence: 95%

Vibrational Spectra and Rotational Isomerism in 2-Mercaptoethanol

Nandy¹,

Mukherjee²,

Roy³

et al. 1973

From the Raman and i.r. spectra of 2-mercaptoethanol in the liquid state and the temperature variation of the intensity of the Raman lines, it has been concluded that both the trans-and garrclleisomers are present in the liquid. A tentative analysis of the vibrational frequencies of the isomers has been presented. D'apres les spectres Raman et i.r. du mercapto-2 Cthanol a 1'Ctat liquide et aussi d'apres la variation en fonction de la temperature de I'intensite des raies du spectre Raman, on peut conclure que les isomtres cis et gauclle existent tous les deux dans le liquide. Une analyse provisoire des frequences de vibration des isomeres est prCsentCe.[Traduit par le journal]Can.