No abstract

The problem of the equilibrium configuration of the ethylene glycol molecule was investigated by measuring the infrared spectra of the vapor (up to 125 "C), liquid, and solid phases between 100 and 3 700 cm-1. The two isotopic molecules (CD2OH)z and (CH2OD)Z were likewise studied. filost of the fundamental frequencies could be observed and assigned. These assignments, as well a s the phase and tenlperature behavior of the spectra, confirm that in all cases the molecules exist only as gauche isomers, which are more stable than the trans as a result of intramolecular hydrogen bonds. Because these bonds are far from linear, the OH stretching vibrations are little affected, but the bending vibrations are strongly shifted towards higher frequencies.Comparison of the calculated thermodynamic functions with the calorimetric data shows that restriction of all three internal rotations in the glycol molecule lowers the entropy by about 10 e.u. a t normal temperature. From the observed torsional frequencies, the average barrier heights are estimated to be of the order of 10 kcal/mole for rotation about the C-C bond, and 3 to 4 kcal/mole for rotation about the C-0 bonds, thereby indicating a fairly rigid structure.On a CtudiC par spectroscopie infrarouge le probleme de la structure molCculaire de llCthyl&ne glycol. Les spectres des trois molCcules isotopiques ( C H~O H ) B , (CHzOD)2 e t ( c D 2 0 H )~ ont Cte mesurCs entre 100 e t 3 700 cm-I B 1'Ctat de vapeur (jusqu'Q 125 "C) ainsi que liquide e t solide.La plupart des frequences fondamentales ont pu &re identifikes. Ces rCsultats, en particulier les effets d e tempCrature e t de changements de phases, indiquent que les molCcules n'existent que sous la forme isomere gauche, laquelle est plus stable que la forme trans b cause de liaisons hydrogkne intramolCculaires. Comme ces liaisons sont loin d'&tre linCaires, les vibrations de valence OH en sont peu affectees tandis que les vibrations de deformation sont fortement dCcalCes vers les hautes frCquences. On a calculC les fonctions d'ktat du glycol par les mCthodes statistiques dans l'hypothbe d'une molCcule rigide. E n comparant ces valeurs avec les donnees calorimCtriques, on constate que l'entropie de la molCcule B temperature ordinaire est abaiss@e de quelque 10 unites du fait de la rotation g&nCe autour des liaisons simples C-C e t C-0. D'aprbs les frequences de torsion on estime la hauteur moyenne des barrihres d e potentiel B quelque 10 kcal/mole dans le premier cas, e t B 3 ou 4 kcal/mole dans les deux autres.

The existence of bifurcated hydrogen bonds (BHB) between three molecules as a major feature of the structure of liquid water was postulated recently to account for the remarkable effect of temperature on the O–H stretching bands in the Raman spectra. As a corollary, there should be two kinds of H⋅⋅⋅O distances in water: one, 1.85 Å, for the well-known linear bonds (LHB), prevalent in cold water, the other, 2.3 Å, for the weaker BHB. This is evident in the neutron diffraction studies of heavy water, which reveal important structural changes with temperature. For instance, the atom pair correlation functions, both in the first-order difference, and the isochoric temperature derivative methods, show two peaks at 1.8 and 2.3 Å, with inverse temperature dependence similar to that of the Raman bands at 3220 (LHB) and 3420 cm−1 (BHB). In the BHB the nearest-neighbor O⋅⋅⋅O distances are the same as in the LHB, but the apex angle is much smaller than the tetrahedral, between 95° and 100°. This allows slightly shorter second neighbor O⋅⋅⋅O distances, and a closer packing of the molecules. The increased average coordination of the H and O atoms creates an imbalance in the stoichiometry of hydrogen bonding. As a result, a few percent of the water molecules are left with one ‘‘free,’’ i.e., nonhydrogen-bonded OH group (NHB). The energy of the BHB is estimated at 2.5 kcal mol−1, i.e., half that of the LHB, and its proportion in the liquid, at nearly 30% at 0 °C. Amorphous ice prepared from the vapor may also contain BHB according to x-ray and neutron diffraction data. The BHB appears as a common feature of hydroxylic compounds; e.g., hydrogen peroxide, alcohols, etc.

The absorption spectra at 25 °C. of aqueous solutions of mineral acids (HCl, HBr, HNO3, HClO4, H2SO4, H3PO4) and of some of their acid salts in various concentrations were measured in the infrared from 2 to 25 µ. In all cases three broad bands were present at 1205, 1750, and 2900 cm.−1 arising from the H3O+ ion. Cooling the samples, and even supercooling them down to liquid air temperature, produced no major changes in the spectra. The bands of the D3O+ ion were also found at 960, 1400, and 2170 cm.−1 in solutions of DCl in heavy water. Thus, the existence of discrete hydronium ions in the liquid state, with average life longer than 10−13 second, is confirmed. Infrared spectra provide a means of estimating the extent of ionization of strong acids in solution.

The rates of thermal decomposition of hydrogen peroxide vapor were measured by the static method at low pressures (0.2 to 20 mm. Hg), over the temperature range 300°–600 °C., in carefully cleaned glass vessels. The reaction was of the first order with respect to time and the final products were only water and oxygen. Around 400 °C. the character of the reaction changed gradually from heterogeneous (surface effects, low activation energy) to homogeneous (reproducible rates in various vessels). With initial pressures of about 10 mm. Hg the experimental rates above 400° lead to an apparent activation energy of 43 kcal. and a frequency factor of 1010.7. After correction for the residual surface decomposition, the rate equation becomes[Formula: see text]in good agreement with the accepted value for the O—O bond dissociation energy. The reaction rates increased regularly with pressure.Packing the reaction vessels with glass rods and adding various gases (including nitric oxide and propylene) had no appreciable effect on the gas-phase reaction. Deuterium peroxide vapor decomposed at the same rate as hydrogen peroxide under comparable conditions. The results may be explained adequately by the following non-chain mechanism for the uncatalyzed decomposition:[Formula: see text]