Spectroscopic Studies of Alcohols: V. Intramolecular Hydrogen Bonds in 2-Cyanoethanol and in Some Nitroalcohols

Abstract

The enthalpy difference between the trans and the intramolecularly hydrogen bonded gauche conformation of 2-cyanoethanol in dilute CCI4 solution is shown to be -0.14 f 0.03 kcal/ mole from the temperature dependence of the fundamental OH stretching bands. At higher concentrations cyclic dimers with double O H . . . O bonds form. The enthalpy change on dimerization is -6.1 f 0.3 kcal/mole. A small percentage of dimers with acylic O H . . .O bonds are also present, but these are thermodynan~ically less stable than the cyclic dimers.Intramolecular hydrogen bonds are found between OH and NO2 groups in some 2-nitroalcohols, 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 ( A H = -0.40 f 0.10 and -0.71 f 0.09 kcal/mole respectively). 2,2-Dinitropropanol and 2-methyl-2-nitro-1,3-propanediol show complex VOH bands due to trans and intramolecularly hydrogen bonded gauche conformers. 2,2,2-Trinitroethanol has a relatively narrow symmetrical OH peak a t teniperatures up to 55 "C which is assigned t o the exclusively populated intramolecularly hydrogen bonded conformation.

Experimental and computational thermochemical study of 3-hydroxypropanenitrile

“…The most stable conformer of 3-hydroxypropaneni- À24.4938 ± 0.0068 T th = 298.15 K; V bomb = 0.380 dm 3 ; p i gas ¼ 3:04MPa; m i water ¼ 1:00 g. m (compound) is the mass of compound burnt in each experiment obtained from apparent mass and corrected taking into account the amount of water in the samples; m 00 (polyethylene) is the mass of polyethylene used in each experiment obtained from apparent mass; m 000 (fuse) is the mass of the fuse (cotton) used in each experiment obtained from apparent mass; T i is the initial temperature rise; T f is the final temperature rise; DT c is the corrected temperature rise; e (calor), energy equivalent of the whole system but the content of the bomb. e trile optimised (gauche I) presents a gauche conformation in order to allow the energetically favourable hydrogen bond as observed in previous experimental studies [37][38][39]. The enthalpy differences at the G3 level obtained in this work and that reported in the literature among all the conformers found are collected in table 6.…”

“…Krueger and Mettee [37] confirmed using IR spectroscopy, that the most stable conformer of 3-hydroxypropanenitrile in dilute CCl 4 is a gauche one stabilised by an intramolecular hydrogen bond from the OH hydrogen to the p cloud, being the enthalpy difference between the gauche and anti conformers of 0.6 kJ AE mol À1 calculated from the temperature dependence of the fundamental OH stretching bands. In the gas phase, Schneider and Giguère [38] determined an enthalpy difference of 2.9 kJ AE mol À1 between both conformers from the infrared spectra of the vapour.…”

Infrared Studies on Rotational Isomerism. V. 2-Nitroethanol

“…This hypothesis has been confirmed definitely by various spectroscopic studies (2)(3)(4)(5). Claims to the contrary (6, 7) were later disproved (4).…”

“…Still, from visual observation it appeared that the relative intensity of the gauche and trans bands did not change nearly as much with temperature as, for instance, in the 2-haloethanols. Under such conditions it was illusory to look for a third 0-H stretching component corresponding to that observed in dilute CCl, solutions (4,5). Conceivably this could be due to a solvent effect.…”

“…Nevertheless, the question of rotational isomerism in the nitroalcohols is not yet completely understood. For instance, 2-nitroethanol in CCl, solutions at high dilution has been reported to exhibit not two, but three distinct 0-H stretching bands arising, presumably, from one trans and two gauche conformers (4,5). The distinction between the latter two is not clearly established.…”