Water OH Groups Research Articles

Near infrared spectroscopic study of the structures of water in proton acceptor solvents.

The structures of water diluted in solvents, which are varied from weak to strong proton acceptors, are discussed from the infrared spectra between 1200 and 7500 cm−1. Three water species are defined without reference to eventual local structures of solvent molecules: in species S0, S1, and S2, the subscript indicates the number of hydrogen bonded OH groups of water. The assignment of the species in every solvent is based on the study of ternary mixtures. It turns out that the fraction of non-bonded water is negligible in all solvents, and that the lifetime of this structure is much shorter than the hydrogen bond residence time at room temperature. The wavenumbers of the non-bonded OH group in species S1 are mainly determined by the local environment and not by the dielectric constant. The ratio K2 = [S2]/[S1] strongly depends on the bulkiness of the base. A relation is found between lnK2 and the number of CH2 or CH3 groups per solvent molecule: it is discussed in terms of entropy and enthalpy of complexation. From the species assignment, the spectral features of species S2 according to the hydrogen bond strength are emphasized. They can be used, with the previously published pattern for species S1, as a guide to determine the state of water in a sample. The contribution of thermal fluctuations to the absorption profiles is considered. It is pointed out that the resolution of absorption envelopes into components of arbitrary shapes, such as Gaussian, should not be related to species without physical argument.

The nature of the ‘free’ OH groups in water

AbstractThe shoulder at the high‐frequency edge of the O‐H stretching bands in the Raman spectra of liquid water is suppressed by addition of about 12 mol% of hydrogen peroxide. This is further evidence for ‘free’ OH groups, i.e. non‐hydrogen‐bonded (NHB), in water, in contrast with liquid hydrogen peroxide. According to a new model, water contains two kinds of hydrogen bonds: the linear bonds (LHB), as in ice, and the bifurcated bonds (BHB) between three molecules. This upsets the ideal 1:1 ratio of proton donor to proton acceptor sites, creating a slight excess of the former, hence the ‘free’ OH groups. Their concentration at room temperature is only of the order of 1–2% from comparison with the spectra of the OH− ion in aqueous solutions. There are no ‘free’ H2O molecules in liquid water.

An infrared-spectroscopic study of reversed micellar solutions of sodium n-octanoate and water in n-decanol

The association process to reversed micelles in the system water/sodium n-octanoate/ n-decanol is studied by means of wave number shifts in the fundamental infrared region. It is found that the antisymmetric vibration band (σ 3), and the scissors vibration band (σ 2) of water, together with the antisymmetric stretching vibration band of the ionised carboxylic groups (σ COO−) are capable of detecting and visualising changes in the micellar association equilibria. The information is primarily qualitative, but some rough quantitative estimations are also made. A comparison between the intensities of the narrow σ 3-line corresponding to unassociated water OH-oscillators discernible at high dilutions in decanol, and the broad σ 3-band of the associated species reveals that the fraction of unassociated OH-groups in water is low, perhaps only a few percent.

A structural interpretation of the differences in the temperature transformation of the bands due to the stretching vibrations of the oh groups of water and methanol

A structural interpretation of the differences in the temperature transformation of the bands due to the stretching vibrations of the oh groups of water and methanol

A spectroscopic investigation of the structure of alcohol-water solutions

The v2 + v3 combination band of water has been recorded for nine alcohol-water solutions in which the volume fraction of water is less than 2% and for three alcohol-water solutions over the entire range of composition. In dilute solutions it was found that the fraction of “symmetrically” bonded water was, in general, smaller than in aprotic solvent-water systems. The fraction of nonbonded water protons was greater in alcohols of higher molecular weight and was also greater in tertiary alcohols than in primary ones. The 2vOH overtone band was recorded for three alcohols in alcohol-rich solutions. Water appears to break up the polymeric alcohol structure, and there appears to be a slight preference for water-water bonds over water-alcohol bonding. Raman spectra of the alcohol C−O stretching mode indicate that water-alcohol bonding is stronger than alcohol-alcohol bonding. The fraction of free alcohol and water OH groups appears to be smaller in solutions of intermediate composition than in the pure liquids. This increased “structure” of the solutions is consistent with the maxima occurring in the viscosity of alcohol-water solutions.

Spectroscopic studies concerning the structure and the thermodynamic behaviour of H2O, CH3OH and C2H5OH

The i.-r. spectroscopic determination of non-H-bonded OH-groups in water and alcohols are in agreement with the thermodynamic behaviour of these liquids. It is possible to calculate the specific heats, the heats of vaporization, the surface energies and the density with these spectroscopic results together with a simple model of the liquids. This method also gives the density maximum and the minimum of the specific heat of H2O. The conformity with the thermodynamic properties shows that these measurements can be employed to develop better theories of liquids and that the approximation methods used for the interpretation of the i.r. spectra are satisfactory.