H-bonded OH Research Articles

Ab initio calculations on the geometry and OH vibrational frequency shift of cyclic water trimer

The equilibrium geometrical parameters R OO θ and χ of cyclic water trimer have been determined at the counterpoise corrected SCF+MP2 level in the ESPB basis within pseudo-C 3v symmetry. The final structure has short ( R OO=2.85 Å) and strongly bent (θ=20°) hydrogen bonds. The non-bonded OH bonds are directed by χ=48° out of the OOO plane. The interaction energy (Δ E) is −14.7 kcal mol −1 and the corresponding D 0=10.2 kcal mol −1. The likely error bars on these results are discussed. The second order polarization interactions in the trimer are markedly non-additive. The total non-additivity contributes −2.0 kcal mol −1 to the final Δ E, and it is responsible for a shortening of R OO by 0.07 Å. Its largest effect (about −70 cm −1) is in the H-bonded OH vibrational frequency shift Δν OH, which at the equilibrium geometry is calculated to be −230 cm −1. The shift is markedly sensitive to the angle χ, and vibrational averaging along this coordinate is expected to reduce Δν. The results therefore support Nelander's reassignment of the IR and Raman gas phase OH spectra, which implies Δν OH≈ −175 cm −1.

Simultaneous absorption of one quantum by two H-bonded OH groups

We have observed simultaneous absorptions in H-bonded liquid methanol. They point to two different H-bonded OH groups and their temperature dependent equilibrium. Their intensities depend on the H-bond orientation.

A variable low-temperature FT-IR study of crystalline β- d-fructopyranose and deuterated analogues

FT-IR spectra have been recorded of β- d-fructopyranose and deuterated analogues at variable temperatures in the range between ambient and 100 K. The natural resolution enhancement showing up in the OH stretching region provides detailed information with respect to the system of H-bonds in the crystalline phase. Other spectral changes resulting from cooling have been studied in addition. The shift of the band maxima proves to be correlated with the H-bond geometry, i.e. the temperature sensitivity depends on the type(s) of H-bonding. The presence of vibrational coupling between some of the H-bonded OH groups has been demonstrated with deuterium exchange experiments. The peaks in the OH stretching region have been tentatively assigned based on the spectral information of the uncoupled vibrations at 100 K.

Contribution to the So-called structure temperature of the electrolyte solutions in methanol based on IR OH band-intensities

The averaged structure temperature T str, as T with similar H-bond structure as the pure liquid, is determined of alcoholic 2.2 m solutions (anions) by IR fundamental integrated intensities. As ion series is got T str: NaClO 4, LiClO 4, LiCl, CsCl, CsF as similar Hofmeister ion series as in water. This method agrees qualitatively with the T str estimations by overtone absorbances and band analysis of non H-bonded OH. Studies of the concentration dependences of T str allows indications on water in the first hydration shell and establish the T str solution studies as useful tool for an average description of solution properties.

Persistent infrared laser induced spectral holes in hydrogen bonded polymers

Persistent spectral holes were burned into the profile of the hydrogen bonded OH stretching absorption, near 3500 cm−1, of three polymeric alcohols. The mechanism is an IR induced conformational change of a H-bonded OH group to weaken the hydrogen bond. In one polymer, an empirical quantum efficiency of about 5×10−3 was measured and a hole depth of 20% of the absorption was achieved with a low power cw laser. The conformational changes occur near the bond which is excited and before extensive intramolecular vibrational randomization.

Structure of salts of arylthioniacycloalkanes with an oxygroup in the benzene ring. XIV. Iodide of hydroxyphenylthionlane. H-bond OH...I

Structure of salts of arylthioniacycloalkanes with an oxygroup in the benzene ring. XIV. Iodide of hydroxyphenylthionlane. H-bond OH...I

H-bonds in methanol—water mixtures: indications of non-H-bonded OH in liquid water

The overtone spectra of water/methanol mixtures are compared with calculated ideal sum spectra with the result that non-H-bonded OH groups are reduced in mixtures. It is indicated that this loss of “free OH” could only originate from liquid water and that therefore the opinion that liquid alcohols contain “free OH” but water does not cannot be established. It is shown that the behaviour of overtone spectra of alcohols and water is similar in the region of non H-bonded OH group absorption. It is discussed how the description of liquid water by the simplified equilibrium of non-H-bonded and H-bonded OH groups contains the mean value of the distance partition.

Caloric properties of liquid alcohols - H-bonded liquids continuum or spectroscopic determined mixture model, is that really the question?

Abstract It is discussed that the spectroscopic based mixture model of H-bonded liquids is qualified as efficient approximation to calculate caloric properties. The specific heat, enthalpy and heat of evaporization of liquid CH 3 OH and C 2 H 5 OH are calculated from the melting point till overcritical temperature with the spectroscopic determined content O f of non H-bonded OH groups and the H-bond energy. The good agreement between the results of water and the two alcohols shows the efficiency of the simplified model although O f , the ratio of van der Waals to H-bond energy and the coordination numbers are totally different in both cases.

Calculations on vibrational properties of H-bonded OH groups, as a function of H-bond geometry

Ab initio calculations on (H 2O) 2 have been performed on 10 model geometries and 17 geometries which simulate OH⋯O contacts encountered in the crystals of β- d-fructose, β- d-arabinose and turanose. The variations with geometry of the hydrogen-bond energy Δ E, the lengthening of the donor OH distance (Δ r), the frequency shift Δν OH and the IR absorption intensity I are investigated. The relation between Δν OH and Δ r is discussed and it is found that most of the observed Δν OH arises from Δ r. It is shown that there is no one-to-one correspondence between Δν OH, Δ E and I. In particular, Δ E may be large even for cases where Δν OH is small. The results are used to determine which OH⋯O contacts give rise to the narrow OH bands observed in the saccharide crystals.

Characterization of surface OH groups on porous glass.

The surface hydroxyl groups on porous glasses pretreated at various temperatures was determined by the successive-ignition-loss method and by means of active hydrogen analyses, and their hydroxyl groups have been classified into two types (isolated and gem type OH groups). The surface of the porous glass consists of three types of OH groups, isolated, gem type and H-bond OH groups. The isolated OH groups were stable up to 500°C, but the elimination of these groups took place gradually above 500°C. On the other hand, the gem type and H-bond OH groups were removed rapidly below 600°C and disappeared above 800°C. The surface of porous glass pretreated at 800°C for 4h contained only isolated OH groups, and the concentration of the isolated OH groups was found to be about 0.7OH's/100Å2. For water vapor adsorption, the surface OH groups play an important role as adsorption sites, and water molecules are adsorbed more strongly on gem type or H-bond OH groups than on isolated OH groups. In porous glass, the ignition-loss method was inadequate to determine the amount of surface OH groups, since water molecules diffused from inside the glass to its surface during heat treatment.

Comparison of calorimetric and IR-spectroscopic data for alcohols and alcoholic solutions

The heats of solution of alcohols in hexane can be considered as the energy necessary to break hydrogen bonds (H-bond). The amount of non H-bonded OH groups estimated from caloric data, are in good agreement with IR-spectroscopic data. Comparison of calorimetric and IR-spectroscopically determined H-bond energies permit the separation of intermolecular van der Waals effects from H-bond interactions. This separation shows that van der Waals interactions of alcohols or water should not be underestimated.

Effect of electrical anharmonicity on the profiles of H-bonded OH and SH stretching bands

The properties of some infrared and Raman bands of OH and SH vibrators engaged in weak hydrogen bonds in the liquid phase at room temperature are studied experimentally as well as theoretically. The differences between isotropic Raman, anisotropic Raman and infrared band profiles are explained in terms of electrical coupling of the XH and X … B stretching modes.

Spectroscopic investigations of the structure of liquid water and aqueous solutions

Abstract IR spectroscopy is a powerful tool for investigating the structure of aqueous systems. Changes in vibrational frequencies and intensities of the absorption band provide information about the structure of the associated water molecules. The water molecule has C 2v symmetry when the intermolecular interaction is symmetrical to both OH bonds as in 2:1 complexes. In this case the frequency difference of the two stretching vibrations ν 3 and ν 1 is nearly constant. If the intermolecular interaction is unsymmetric to the OH bonds as in 1:1 complexes the band separation of ν 3 and ν 1 increases markedly in relation to the increase of the unsymmetry. The IR overtone region is more suitable for the study of the structure of liquid water or aqueous solutions than the IR fundamental region. The reason is the higher intensity of the absorption bands of the “free” OH vibration compared to the H-bonded OH groups. The ratio of the intensities is inverse in the fundamental region. Furthermore it is possible to measure quantitatively in the overtone region and there are no experimental difficulties. The results are estimations of the H-bonded and the free OH groups in different aqueous systems.

Infrared study and thermodynamics of hydrogen bonding in tri- and tetra-methylene glycol monomethyl ethers

Tri- and tetra-methylene glycol monomethyl ethers in very dilute carbon tetrachloride solutions (C < 0.025 mol dm–3) exhibit free OH bands at ∼ 3630 cm–1 and intramolecularly H-bonded OH bands at ∼3540 and 3450 cm–1 respectively. The thermodynamic quantities involved in the MI⇌ MF equilibria are: ΔH°= 15 kJ mol–1, ΔS°= 52 J K–1 mol–1 and K(at 298 K)= 1.4 for trimethylene glycol monomethyl ether. For tetramethylene glycol monomethyl ether ΔH°= 18 kJ mol–1, ΔS°= 68 J K–1 mol–1 and K(at 298 K)= 2.2. In the concentration range 0.02–0.20 mol dm–3, the self-associated species are found to form a mixture of open + closed dimers and trimers while above 0.2 mol dm–3 higher associated species are present. The self-association behaviour of these compounds is thus similar to that of simple alcohols.

Structural Arrangement of Functional Groups in Soil Humic Acid as Revealed by Infrared Analyses

AbstractHumic acid from a brunizem soil was subjected to a series of treatments (methylation, saponification, acetylation) to determine the number and arrangement of functional groups when analyzed by a combination of chemical and infrared techniques. One‐third of the COOH groups (total COOH, 390 meq/100 g) occurred in positions close enough to form cyclic anhydrides; two‐thirds of the OH groups (total OH, 290 meq/100 g) were phenolic. Some phenolic OH groups in the samples failed to methylate wth diazomethane. Potassium bromide catalyzed the formation of cyclic anhydrides by mild thermal treatment of acid‐treated and methylated‐saponified humic acids, but not of untreated humic acid. Acetylation gave a small amount of brown material (acetyl content, 20%) whose infrared pattern was characteristic of an acetylated carbohydrate. Tests for quinone and H‐bonded phenolic OH groups were negative.