OH Frequency Research Articles

ChemInform Abstract: MOLECULAR MECHANICS CALCULATION ON THE HYDROXYL STRETCHING FREQUENCY IN SATURATED ALCOHOLS

Abstract The frequencies of the hydroxyl stretching vibration, ν OH , of the OH rotamers of methanol, ethanol, propan-2-ol, t-butanol and adamantan-1-ol in the gas phase have been calculated applying molecular mechanics methods. A discussion is devoted to the assignment of the observed ν OH frequencies to the rotamers in ethanol and propan-2-ol in view of the discrepancy in published data. The calculations were performed with the Allinger MM2 force field. It proved to be necessary to include electrostatic interactions between point charges located at the atomic nuclei to obtain calculated results that are in good agreement with experimental measurements. The calculation of these interactions and the introduction in the minimization procedure of the energy is described. Minor adaptation of the force field was needed to fit the observed frequencies. With the introduced modifications a systematic increase of about 0.3 kcal mol −1 is found in the calculated steric energies of the conformers. The relative rotamer populations derived from the energy difference between OH conformers in the molecules ethanol and propan-2-ol agree with experimental IR results.

Molecular mechanics calculation on the hydroxyl stretching frequency in saturated alcohols

The frequencies of the hydroxyl stretching vibration, ν OH, of the OH rotamers of methanol, ethanol, propan-2-ol, t-butanol and adamantan-1-ol in the gas phase have been calculated applying molecular mechanics methods. A discussion is devoted to the assignment of the observed ν OH frequencies to the rotamers in ethanol and propan-2-ol in view of the discrepancy in published data. The calculations were performed with the Allinger MM2 force field. It proved to be necessary to include electrostatic interactions between point charges located at the atomic nuclei to obtain calculated results that are in good agreement with experimental measurements. The calculation of these interactions and the introduction in the minimization procedure of the energy is described. Minor adaptation of the force field was needed to fit the observed frequencies. With the introduced modifications a systematic increase of about 0.3 kcal mol −1 is found in the calculated steric energies of the conformers. The relative rotamer populations derived from the energy difference between OH conformers in the molecules ethanol and propan-2-ol agree with experimental IR results.

On the structure of calcium—lead phosphate apatites

In order to obtain information about the structure of Ca 10- x Pb x (PO 4) 6(OH) 2 (O< x<10) compounds, powder X-ray diffraction patterns and i.r. absorption spectra have been studied. Solid solutions of the complete series have been obtained and lattice parameters dimensions and cation distribution in unequivalent sites are given. OH, PO 4, CO 3 and cation oxygen fundamental frequencies were assigned.

Infrared spectra of calcium-strontium phosphate apatites

The ir spectra of calcium-strontium phosphate apatites were studied and the OH, PO 4, CO 3, and cation-oxygen fundamental frequencies were assigned. Furthermore, X-ray diffraction patterns were obtained and lattice parameters were calculated.

OH stretching frequencies of solid hydroxides and of free OH − ions

The vibrational frequency of free OH − ions, which cannot be directly measured, has been claimed to be 3700 cm −1. In solid hydroxides the OH stretching frequency has been found in the range from 3690 to 3100 cm −1. The decrease of the vibrational frequency has been interpreted to be caused by hydrogen bridges or the increase of the metal oxygen bond strength. We suggest an alternative explanation. The vibrational frequency of unperturbed OH − ions is 3570 ± 10 cm −1. In ionic hydroxides this frequency is increased due to repulsion effects of the lattice or decreased if hydrogen bonds are present, to a large extent (up to 400 cm −1) in the case of common OH −….X bridges and only up to 70 cm −1 in the case of XH….OH − bonds.

Stretching vibrations of water in isotope-diluted ferroelectric potassium ferrocyanide trihydrate

A partially deuterated and a pure K 4Fe(CN) 6 · 3H 2O crystal have been investigated by low-temperature Raman and IR spectroscopy. Five unperturbed OH frequencies of the HDO molecules were found and are discussed in comparison with the corresponding OD frequencies obtained previously. The temperature behaviour of both unperturbed and perturbed OH(OD) modes has shown that not the isotope isolation but the dynamic disorder of the crystal is the major contributor to the spectral bandwidths.

IR-absorption study of H and D-impurities in BaTiO3crystals

Abstract The temperature dependence and polarization of five bands due to OH-vibrations in poled BaTiO3 single crystals yield information leading to a microscopic model for the position of the hydrogen in the host lattice. Values for the anharmonic contribution to the localized oscillation are deduced from the overtone frequency of OH and the isotrope shift of the OH/OD stretching vibration.

Role of structure in transport across membranes

Interactions between water and two polymers used in membrane technology which are cellulose acetate (39.8% acetyl content: CA) and poly-trans-2, 5-dimethyl piperazinthiofurazanamide (DMP-TFZ) are presented. Experimental adsorption isotherms are discussed on the basis of BET, Zimn, Flory-Huggins theories. DMP-TFZ shows a lower water cluster formation tendency than CA at low and mean activities. The state of water was studied also by IR: in both the polymers the adsorbed water stretching OH frequencies are shifted to higher values showing weaker H bonds than in water. This can be related to the existence of water in the state of monomer and small size aggregates and favours high mobility. The structure of CA dense films is amorphous to X rays, but a certain amount of crystallinity is revealed by DTA. DMP-TFZ is amorphous to X rays, has a high T and shows high stiffness to mechanical dynamical tests. The suggestion is made that stiff chain polymers which contain hydrophilic groups and which cannot easily crystallize, but can get a close packing, do not allow the formation of big free volume packets across which large size water clusters, able to solvate ions, can move.

Monitoring of OH maser emission from late-type stars

Eight OH-IR stars have been monitored at the satellite- and main-line frequencies of OH. Problems are addressed relating to the pump mechanisms responsible for the maser inversion, the degree of saturation of the masers, and the linear dimensions of the circumstellar shell. The following conclusions have been reached. The satellite- and main-line masers are both radiatively pumped, almost certainly by infrared photons. The OH lags the optical emission by 10-50 days. The data suggest that the linear dimension of the shell is a few times 10 to the 16th cm, in agreement with theoretical predictions. The satellite-line masers are always saturated, but the main-line masers may or may not be. In addition, the anomalous source U Ori is studied. By combining the present data with those of Cimerman (1979), it is shown that the 1612-MHz maser emission of this source follows the optical emission through individual cycles but at reduced mean intensities for each successive cycle.

NMR study of adsorbed water. II. Molecular motions in the monolayer hydrate of halloysite

In the electrically neutral interlayer space of endellite, the water monolayer does not exhibit a preferential orientation such as that observed in phyllosilicates with water hydrating the interlayer cations (see, for example, the first paper in this series). The influence of the surface is to provoke an anisotropy of the molecular motions which can be separated into a rapid 180° flipping motion about the C2 axis and a slow tumbling about an axis perpendicular to C2. The activation energy of the former motion is 4.6 kcal mole−1, whereas that of the latter is 3.6 kcal mole−1. The proton and deuteron spin–spin and spin–lattice relaxation times can be accounted for by this simple model. Two other types of experimental results complement this model. The observed infrared OH frequencies suggest weak hydrogen bonds between water molecules and surface lattice hydroxyls, whereas strong hydrogen bonds lock water molecules to each other. The molar heat capacity of adsorbed water parallels that of ice up to the temperature (130 °K) where a torsional motion about the C2 axis is transformed into the 180° flipping motion.

Study of the interaction between surface hydroxyls and adsorbed water molecules on porous glasses by means of infrared spectroscopy

Infrared absorption spectroscopy was employed to investigate the interaction between surface hydroxyl groups and adsorbed water molecules. Firstly, after a confirmation of the well-known frequencies of OH, H 2O and OD, D 2O vibration bands for the present system, the spectrum of adsorbed HDO molecules was studied. On this basis, the vibration of those surface hydroxyls which interact with adsorbed water was analyzed for the fundamental and first overtone OH stretching modes. These frequencies were used to estimate dissociation energies of interacting surface hydroxyls (118 kcal/mole) supposing that their potential curve can be described with sufficient accuracy by a Morse function as in the case of free OH groups. This high barrier for a formation of free protons is in contrast to the small activation energy (about 5 kcal/mole) for the proton life-time with respect to an exchange between surface hydroxyls and adsorbed water according to nmr data. This result rules out an exchange mechanism in which an classical H 3O + structure participates. Rather it points to a mechanism in which OH bands of the hydroxyl and the water molecule change places simultaneously, i.e. a synchronous reaction.

Self association behaviour of α-ω diol monoalkyl ethers

The infrared spectroscopic and thermodynamic properties of H bonding in a number of diol monoalkyl ethers RO(CH2)nOH and RO(CH2)2O(CH2)2OH where R = CH3, C2H5 and C4H9 and n= 2, 3 and 4 are rationalised in terms of their conformational and self-association behaviour in solutions. The half-band width Δtext-decoration:overlineν½ and the apparent integrated absorption intensity B= 1/Cl∫ ln(T0/T)text-decoration:overlineνdtext-decoration:overlineν of the intramoleculary H bonded OH bands and the enthalpy change ΔH° involved in the equilibrium reaction intramolecularly H bonded monomer ⇌ free monomer are linearly correlated with the shift of OH frequency on intramolecular H bonding Δtext-decoration:overlineν(=text-decoration:overlineνfree OH–text-decoration:overlineνH bonded OH). The nature of the self-associated species is found to depend no the stability of gauche conformations of the O(CH2)nO units.

Rotational isomerism—22 : An nmr study of oh..π bonding and the conformations of benzyl alcohol and derivatives

The conformations of benzyl alcohol, the ortho and para nitro and methoxy derivatives and benzyl methyl ether have been investigated by NMR in CCL 4 and DMSO solutions. The 3J(CH.OH) and 2J(H.C.H) couplings (the latter via the 2J(H.C.D)coupling)and the OH chemical shift (in DMSO and ∞ dil XXX as conformational probes. The δ ∞ (OH) for ROH (R = Me, Et, iPr) is also given. The results provide no support for the existence of an intramolecular H-bond in benzyl akohol The endo conformation of the OH proton ( anti to a CH proton) is favoured by ca. 1 kcal mole −1 over the exo conformation (H anti to phenyl) and these conformers are responsible for the separate OH frequencies observed in the IR spectrum. The results do not support an extreme conformation of the phenyl ring (C.C.C.O dihedrals of 0 or 90°) but are consistent with either an 6̃0° conformation of the phenyl ring or a freely rotating model. In ortho nitrobenzyl alcohol intramolecular H-bonding is present, but in ortho methoxy benzyl alcohol little or no bonding to the substituent occurs.

Infrared spectroscopic study of the interaction between 2,6-diarylphenols and alkyl cyanides

The O–H stretching absorptions of 2,6-diarylphenols are composed of two symmetrical bands (intramolecular OH ⋯π and intermolecular OH ⋯ N interactions) in the presence of alkyl cyanides in carbon tetrachloride solution.The equilibrium constants K for the competitive interactions were determined. The equilibrium study suggested that the K values depend on the dihedral angle between the phenol ring and the 2,6-aryl groups. Comparison of log K with ν0(OH)(the frequency of the OH ⋯ N band at infinite dilution in CCl4) revealed a linear relation. Furthermore it was found that the frequency shifts caused by the concentration of cyanide can be explained by the Kirkwood-Bauer-Magat relationship.

Influence of solvents on the -OH and stretching frequencies of benzoin and methyl mandelatestretching frequencies of benzoin and methyl mandelate

The influence of solvents on the intramolecular hydrogen bond in benzoin and methyl mandelate is studied using infrared spectroscopy. Non-oxygenated solvents could not break the chelation but could shift the OH frequencies to a small extent. Oxygenated solvents like diethyl ether, acetone and dioxan could break the chelation and form intermolecular hydrogen bonds. The relative intensities of the bands of intra and intermolecular hydrogen bonds gave an indication of the donor ability of these solvents, which is linked with their capacity to break the intramolecular hydrogen bonding. Making use of the symmetry numbers of the OH band, the order of the interacting abilities of the oxygenated solvents in breaking the chelation is ascertained and explained.

Effets de substituant sur la fréquence hydroxyle de phenols associés à des hydrocarbures benzéniques par liaison d'hydrogene

The electronic effects of X substituents in aromatic molecules XC 6H 5, XC 6H 4Me and XC 6H 4OMe are studied by measurements of the bonded OH frequencies of phenol-π-base complexes. A judicious choice of the experimental conditions (solvent, π-base concentration, phenol acidity, temperature) permits the following substituents to be studied: Me, Et, CH(Me) 2, OMe, OEt, OC 6H 5, NHMe, N(Me) 2, N(Et) 2, NHC 6H 5, C 6H 5, CHCH 2, CCH, CCMe, SMe, SC 6H 5, F, Cl, Br and I. Halogenated benzenes, benzotrichloride and benzotrifluoride were found to act solely as π-bases. Electronic effects are accurately measured by means of the linear combination ϱ 1σ 1 + ϱ Rϱ° R. The ratio ϱ R/ϱ 1 shows that inductive and mesomeric effects are of the same importance. This ratio may be considered as an argument in favour of the symmetric configuration of the complex. Electronic effects are found to be additive in disubstituted benzenes.

An infrared study of various nitrated polysaccharides and their structural characterisation

Infrared absorption spectra for a number of polysaccharides and their nitrated derivatives have been obtained. The frequency range 730–960 cm −1 is useful for identification of the polysaccharides, and the region 900–1350 cm −1 is more suitable for distinguishing the nitrated materials. The strong intensity of the nitrate bands limits the interpretation of spectra below 960 cm −1, but above this frequency the absorption bands of nitrated polysaccharides are generally sharper and more clearly defined than the corresponding bands of the parent polysaccharides. Data on the COC bridge, CC ring, CO, and COH frequencies and on the CH deformation and stretching frequencies have been obtained. The use of i.r. spectroscopy for the quantitative determination of nitrate groups in nitrated polysaccharides is discussed.

Monomeric OH Stretching Frequencies in Monohalogenated Monocarboxylic Acids

In a recent publication from these laboratories we discussed spectra-structure correlations for pure monohalogenated monocarboxylic acids and noted that the bonded OH stretching vibration appeared to undergo a frequency shift in certain of the compounds studied. The extreme broadness of these absorption bands prevents accurate peak frequency measurements. We have now measured the frequencies of the monomeric OH stretching frequencies of these compounds in carbon tetrachloride solution, along with those of a few unsubstituted acids for comparison, and report the results here.

Infrared spectrum of HDO in aqueous solutions of perchlorates and tetrafluoroborates

The OH and OD stretching bands of HDO in aqueous solutions containing the ions ClO4− and BF4− are split into two components. The high-frequency component, A, does not shift with temperature. It is interpreted as due to OH groups involved in weak [Formula: see text] or [Formula: see text] hydrogen bonds. This interpretation is in line with the corresponding OH frequencies of other systems containing ClO4− ions, such as methanolic solutions and crystalline hydrates. Solvent-separated ion pairs may account for the observed cation effect on band A. The low-frequency component, B, varies with temperature almost exactly like the corresponding band of pure water. It is interpreted to be due to those OH groups which are not associated with the anion. Components A and B are not resolved in solutions of most electrolytes because the distribution of strengths of interactions of OH groups with most anions overlaps that of [Formula: see text] interactions between water molecules.

Stretching Frequencies of Structural Hydroxyls of Hectorite and K-Depleted Phlogopite as Influenced by Interlayer Cation and Hydration

AbstractThe frequencies of structural OH stretching vibrations in swelling trioctahedral minerals such as hectorite or K-depleted phlogopite depend on the ionic form and hydration of the sample. The trioctahedral structure is evidently a suitable case for the observation of spectral changes, since hydroxyl groups are in conditions of high reactivity with the surrounding medium. These changes are attributed to the field which originates either from the cations or the residual water molecules, and the joint analysis of spectroscopic and X-ray diffraction data permits an interpretation that frequencies quoted for unaltered mica are only perturbed frequencies.