Hydrogen-bonded Species Research Articles

A quantitative Raman spectroscopic investigation of hydrogen-bonding in ethanol and ethanol-d1

Abstract The intensity of the band in the Raman spectra of liquid ethanol and ethanol-d1 at Δ ν =270 cm−1 was used to determine the enthalpy of hydrogen-bond formation between non-bonded and hydrogen-bonded alcohol species over the temperature range 156 to 347 K. The following enthalpy values were determined: • ΔH0EtOH= −10.5±0.1 kJ mol−1 • ΔH0EtOD= −12.6±0.2 kJ mol−1. These values are similar to those quoted in the literature for the enthalpy of formation of a single hydrogen-bond and confirm that there is one hydrogen-bond per molecule of ethanol over the temperature range studied.

Hydrogen bonding in 3-azetidinol—3. Ab initio and experimental spectra of the hydrogen-bonded species

Abstract The IR and Raman spectra in the range 4000-10 cm − of 3-azetidinol and the O,N-dideuterated derivative have been recorded in the solid state and in aqueous solution. The interpretation of the vibrational spectra has been based upon ab initio calculations in the STO-3G approximation. A model structure for the calculations has been adopted in which 3-azetidinol binds two molecules of water and two molecules of ammonia. The results obtained for the aqueous solution are in accordance with the occurrence of 3-azetidinol as a hydrated, stacked, intermolecularly hydrogen-bonded chain.

A Fourier-transform i.r. study of ethene adsorbed on HZSM-5 zeolite at low temperature (295 K)

Fourier-transform i.r. studies of ethene on HZSM-5 zeolite at 295 K have demonstrated the presence of hydrogen-bonded interactions at three different hydroxyl sites. Detailed studies of the adsorption isotherms indicate, however, that the strengths of the interaction are different at the different sites. The ethene is severely perturbed, as evidenced by the appearance of i.r. forbidden (A g ) bands, but only one perturbed species can definitely be identified. This hydrogen-bonded species has a rate of reorientational motion which is greatly reduced from that in the liquid phase.

Excitation Wavelength Dependence of Phosphorescence and Hydrogen-Bonding Formation of Thioxanthone and 2,4-Diisopentylhioxanthone

Abstract Phosphorescence spectra of the ethanol solutions of thioxanthone(TX) and 2,4-diisopentylthioxanthone (DITX) exhibited excitation wavelength dependence at 77 K. In addition to the normal phosphorescence observed at 450 nm for TX and at 460 nm for DITX, a new red-shifted phosphorescence was resolved at 470 nm and 485 nm, respectively, when TX and DITX were excited at the absorption tail. The lifetimes and excitation spectra of the red-shifted phosphorescence were found to differ from those of the normal phosphorescence. Based on the study on UV absorption spectra and phosphorescence spectra measured with hydrated species of TX and DITX in ethanol–water solution at 77 K, the red-shifted phosphorescence is ascribed to the hydrogen-bonded species with water. In 2-methyltetrahydrofuran, phosphorescences of TX and DITX shift to the longer wavelengths and the lifetimes become longer when excited at the longer absorption tail, although the phosphorescence excitation spectra do not change appreciably.

Infrared spectroscopic observations of hydrogen bonding and Fermi resonance of adsorbed methyl chloride on alumina surfaces

The physical adsorption of methyl chloride onto Al2O3 surfaces containing surface OH groups has been studied using transmission infrared spectroscopy. Methyl chloride reversibly bonds via hydrogen bonding to the surface hydroxyl groups with a spectroscopically measured heat of adsorption of −3.37±0.38 kcal mol−1. Physisorption of methyl chloride results in a significant reduction in the intensity of the rotational wings of the methyl chloride absorption bands relative to the gas phase, a small downward frequency shift in their band centers, and substantial effects on the ν(OH) region of the alumina spectrum due to hydrogen bonding of surface OH groups with methyl chloride. Fermi resonances are observed for adsorbed methyl chloride and result in the observation of the overtones of both the symmetric and asymmetric methyl deformation modes. It is postulated that the hydrogen-bonded CH3Cl species possess rotational (or other) degrees of freedom which lead to a high entropy in the adsorbed layer, compared to the liquid.

FT-i.r. study of hydrogen bonding in coal

Hydrogen bonding is thought to play a key role in the structure of many coals and has a significant effect on many properties. However, there has been little discussion on the precise nature of the hydrogen-bonded species present. Infrared spectroscopy is perhaps the most sensitive tool for probing hydrogen bonds and in this study band assignments and the importance of hydrogen-bonded groups in coal will be discussed.

Rotational, structural, ab initio, and semirigid bender analysis of the millimeter wave spectrum of H 2COHF

The hydrogen-bonded species H 2COHF has been studied in a conventional microwave absorption cell. The dimer was produced under equilibrium conditions at −78°C from a mixture of H 2CO and HF. Spectra from H 2COHF, H 2CODF, and D 2CODF are reported. Rotational spectra from two low-energy excited vibrational states, which involve the hydrogen bond, have been observed. Structural analysis was performed by fitting rotational constants after correcting the observed rotational constants for contributions from the low-energy vibrational states. The semirigid bender model was fitted to the observed rotational structure of the bending vibrational levels. The bending potential function and the intermolecular distance were determined in the fittings. SCF ab initio calculations were used to model the bending vibrational dynamics and the potential functions of the three in-plane intermolecular vibrations.

Computer simulation of quenched liquids: the glassy state of water

Monte Carlo simulation of liquid water quenched to low temperatures has been carried out in the NPT ensemble. The quenched system shows a glass-like transition and a distribution of hydrogen-bonded species different from the liquid.

Vibrational circular dichroism in hydrogen bond systems: Part II. Vibrational circular dichroism of the OH stretching vibration in 2,2-dimethyl-1,3-dioxolane-4-methanol

Vibrational circular dichroism (VCD) of the OH stretching band in 2,2-dimethyl-1,3- dioxolane-4-methanol has been studied. The OH stretching vibration for the intramolecularly hydrogen-bonded species in the (R)-enantiomer gives rise to a positive VCD band but no VCD band for the hydrogen-bond free species. It is shown that the G −G + conformation in the intramolecular hydrogen bond system ▪ gives a positive VCD band for the OH stretching vibration. The thermodynamic parameters in equilibrium between the free and intramolecularly hydrogen-bonded species have been determined as Δ H =−7.8 kJ mol −1 and Δ S = −18 kJ K −1 mol −1.

An a b i n i t i o investigation of possible intermediates in the reaction of the hydroxyl and hydroperoxyl radicals

A b initio quantum chemical techniques have been used to investigate covalently-bonded and hydrogen-bonded species that may be important intermediates in the reaction of hydroxyl and hydroperoxyl radicals. Stable structures of both types were identified. Basis sets of polarized double-zeta quality and large scale configuration interaction wave functions have been utilized. Based upon electronic energies, the covalently-bonded HOOOH species is found to be 26.4 kcal/mol more stable than the OH and HO2 radicals. Similarly, the hydrogen-bonded HO---HO2 species is found to have an electronic energy 4.7 kcal/mol below that of the component radicals, after correction is made for the basis set superposition error. The hydrogen-bonded form is found to be planar, to possess one relatively ‘‘normal’’ hydrogen bond, and to have lowest energy 3A′ and 1A′ states that are essentially degenerate. The 1A″ and 3A″ excited states produced by rotation of the unpaired OH electron into the molecular plane are found to be very slightly bound.

Hydrogen bonding. Part 1.—Equilibrium constants and enthalpies of complexation for monomeric carboxylic acids with N-methylpyrrolidinone in 1,1,1-trichloroethane

A novel calorimetric method has been derived for the simultaneous determination of equilibrium constants and enthalpies of complexation of monomeric carboxylic acids with bases in an inert solvent. The method requires a knowledge of the corresponding equilibrium constants and enthalpies for the monomer/dimer equilibrium in the same solvent. Both sets of K° and ΔH° values have been obtained for a number of carboxylic acids (and some other hydrogen-bond donors) in 1,1,1-trichloroethane at 298 K, using N-methylpyrrolidinone as a standard base. For the first time, it is possible to evaluate the relative hydrogen-bonding strength of monomeric carboxylic acids and other hydrogen-bonding species in an inert solvent. It is shown that unactivated carboxylic acids are no stronger than simple phenols: equilibrium constants for hydrogen bonding towards N-methylpyrrolidinone are acetic acid (109), benzoic acid (118) and phenol (137). It is further shown that the monomeric carboxylic acids are ca. 20 times as strong as the dimeric acids towards N-methylpyrrolidinone (NMP) in 1,1,1-trichloroethane, with respect to the formation of the species RCO2H·NMP in each case.

Intramolecular hydrogen bonding and intermolecular association of amino alcohols

Infrared spectral studies of the hydrogen-bonding behaviour of aminoethanol and aminopropanols have revealed that they form the strongest intramolecular hydrogen bonds among the substituted alcohols X(CH2)2,3,4OH where X = F, Cl, Br, I, OH, OCH3I, NR2(RH, alkyl) in a given series, establishing the importance of basicity in the hydrogen-bonding interaction. Strong intramolecular hydrogen bonding was found to reduce considerably their association tendency so that there were large amounts of intramolecularly hydrogen-bonded species in concentrated solution. The limited numbers of associated species formed were largely composed of closed dimers, whose nature depended on the strength of intramolecular hydrogen-bond. In dimethylaminoethanol and 3-aminopropanol, the dimers involved the participation of nitrogen so that fairly large ring dimers (ten- and twelve-membered, respectively) were formed. In the case of diethylaminopropanol, since the intramolecular hydrogen bond was very strong, the intermolecular association was limited to small amounts of free hydroxy monomers.

Infrared studies and thermodynamics of hydrogen bonding in 2-halogenoethanols and 3-halogenopropanols

From a non-linear least-squares curve analysis of the spectra of 2-halogenoethanols and 3-halogenopropanols in the hydroxy stretching region in dilute carbon tetrachloride solution at 298–338 K, the thermodynamics of the equilibrium between free and intramolecularly hydrogen-bonded species have been determined. The amount of intramolecularly hydrogen-bonded species decreased with increasing size of halogen and increasing steric repulsion. The similar frequency shifts of the intramolecularly hydrogen-bonded hydroxy group in both the 2-halogenoethanols (17–50 cm–1) and 3-halogenopropanols (15–52 cm–1) established the poor proton-acceptor properties of the halogens, including the highly electronegative fluorine. The absence of intramolecularly hydrogen-bonded species in 4-chlorobutanol is a case where the entropy change over-rides the enthalpy change due to hydrogen bonding. Hydroxy frequency shifts due to intramolecular hydrogen-bonding ran opposite to the enthalpy changes disobeying Badger–Bauer rule. These alcohols associate forming dimers (ca. 3500 cm–1) in which the hydroxy groups alone participate in intermolecular hydrogen bonding.

Effect of molecular interactions on the O-H stretching force constants for associated water species

Semi-empirical molecular-orbital calculations are reported for the O-H stretching force constants of different hydrogen-bonded species of water involving dimeric, trimeric, tetrameric and pentameric associations. These calculations show that - in general - a water molecule bonded to another water molecule through oxygen lone-pair electrons behaves as a stronger acid than an isolated water molecule, and a water molecule bonded to two water molecules through its two oxygen lone pairs is still stronger. This is reflected in the force constants of hydrogen-bonded O-H bonds. These results explain why O-H stretching bands in IR and Raman spectra of liquid water appear at significantly lower frequencies than for solutions of water in organic bases, even though water is a weaker base.

Crystal and molecular structures of two polymorphic forms of dimethyl-N-(2-ethylphenyl)-phosphoramidate (I) and dimethyl-N-(2,6-dimethylphenyl)-phosphoramidate (II)

The crystal structures of the phosphoric amides dimethyl-N-(2-ethylphenyl)-phosphoramidate (I) and dimethyl-N-(2,6-dimethylphenyl)-phosphoramidate (II) have been determined by direct methods and refined by full-matrix least squares. Compound (I) crystallizes in two polymorphic forms, both monoclinicP21/c, but with different cell parameters. Parameters for compound (I) are: FormA:a=10.878(5),b=8.890(4),c=25.11(1) A,β=92.18(2)°; FormB:a=7.071(4),b=17.059(9),c=10.221(5) A,β=97.07(2)°. Compound (II) is also monoclinicP21/c witha=8.453(4),b=14.231(7),c=10.283(5) A,β=108.95(2)°. Compound (I) exists as a hydrogen-bonded dimer, whereas compound (II) exists as a hydrogen-bonded polymeric species.

Vibrational relaxation and νs(AH) absorption band profiles of weak hydrogen-bonded complexes in liquids

Abstract The ν > (AH) IR absorption band profile of a weak hydrogen-bonded complex AH … B embedded in liquid is calculated within the two-mode (ν > (AH)) and ν AB coupling scheme. The generalized Langevin equation is invoked to describe the dynamics of the low-frequency (harmonic) ν AB oscillator influenced by the random force from surrounding molecules. The main goal is to take account of not very short correlation times τ c of this force, which is likely to be the case in real liquids. The non- zero τ c value results in an appearance of a purely dissipative mode when A and B approach each other. This is shown to be responsible for the ν > (AH) bandshaping in the hydrogen-bonded species exhibiting ν > (AH) band halfwidths smaller than or of the order of the ν AB vibration frequency. As for the ν AB absorption band profile, it is formed by the damped oscillatory A→ ← B motional mode. The relationships connecting the characteristics of the ν > (AH) and ν AB bandshapes are obtained. It is shown that such entities as the mean-squared A … B length dispersion in solution, the mean-squared fluctuating force acting on the ν AB oscillator and its correlation time τ c can be estimated from the joint analysis of the experimental ν > (AH) and ν AB band profiles. Comparison with the experimental data for phenol(OD)-pyridine in CCl 4 yields τ c = (O.6–1.0)x10 −2 s.

Effect of papulacandin B and calcofluor white on the incorporation of mannoproteins in the wall of Candida albicans blastospores.

Incorporation of mannoproteins into the walls of Candida albicans blastospores (yeast phase) was followed by continuous labelling and pulse-chase experiments. The effect in the process of compounds that interfere with synthesis (papulacandin B) or assembly (calcofluor white) of structural polymers was also assessed. Mannoproteins which are kept in place by non-covalent bonds (mainly hydrogen bonds) were incorporated rapidly after their release into the periplasmic space, this process being blocked by calcofluor white. The stain had no effect on the incorporation of covalently linked mannoproteins. Papulacandin B inhibited formation of beta-glucans and incorporation of covalently linked mannoprotein molecules, whereas incorporation of hydrogen-bonded species took place normally. The results suggest that the formation of the non-covalent bonds between the mannoproteins occurs once they are secreted into the periplasmic space, whereas the formation of covalent connections between mannoproteins and wall glucan takes place at the level of the plasma membrane.

Ultraviolet resonance Raman studies of N-methylacetamide

Resonance Raman spectra of the simple peptide model compound N-methylacetamide have been obtained with 218- and 200-nm laser radiation. A large enhancement of the amide II vibration is observed relative to that of Raman spectra obtained with visible radiation. Replacement of the amide hydrogen by deuterium results in a spectrum with most of its intensity in the amide II' mode. Excitation of this deuterated species with 200-nm radiation results in intensity in the overtones of this modes, a feature characteristic of resonance enhanced spectra. Isotopic substitution of the amide carbon and nitrogen by /sup 13/C and /sup 15/N results in a spectral shift to lower frequency by nearly the amount expected for a normal mode consisting primarily of the motion of the amide C and N atoms. These results, taken together, demonstrate that the geometry change of N-methylacetamide upon electronic excitation to the ..pi..-..pi../sup */ state is dominated by a change in the C-N bond length. Studies of mixtures of the deuterio and protio forms show that a significant normal mode rotation occurs on isotopic substitution such that the amide II' of the deuterio form becomes approximately equally distributed between the amide II and III vibrations of the protio form.more » The amide I and I' vibrations are very diffuse in aqueous solutions at the dilutions used. These bands become sharp in acetonitrile. This behavior is interpreted in terms of a range of frequencies for this vibration due to a distribution of hydrogen-bonded species. 23 references, 5 figures.« less

Thermodynamics of solutions of propanols in nonassociating components

The spectroscopic and thermodynamic properties of solutions of propanols in various nonassociating components can be described well by an associated solution model in which the association of alcohol molecules into open-chain and cyclic hydrogen-bonded species and the formation of complexes between the terminal hydroxyl group of the alcohol chain molecules and a solvating component are taken into account, with allowance for a non-polar interaction term. Ternary predicted values of vapor—liquid equilibria and excess enthalpies for mixtures including propanol and two nonassociating components are in good agreement with experimental results.

Evidence for the existence of hydrogen-bonded cyclic tetramers in aqueous solutions of tetramethylammonium guanosine 5′-monophosphate

Proton NMR and FTIR measurements have shown that the formation of stable, interbase hydrogen-bonded species of 5′-GMP in aqueous solutions of the tetramethylammonium salt can occr without the subsequent formation of ordered, slowly-exchanging structures or base stacking. Analysis of the NMR data is in agreement with an equilibrium mixture of monomers, dimers and cyclic tetramers. The association constants and amino proton chemical shifts are reported for these species. This is the first report that the cyclic tetramer structure exists as a discrete species in 5′-GMP solutions.