Hydrogen bonding and molecular association in methylated 3-hydroxypyridines

Association in derivatives of 3-hydroxypyridine has been examined via the chemical shifts for OH in PMR for equimolar mixtures of the derivatives of pyridine and phenol in CCl₄ and CH₂Cl₂. It is found that spatial screening of the pyridine N and phenol OH by methyl groups has an anomalous effect on the strength of the complex. A possible explanation is that the ionic form NH . . . O is stabilized on account of increased basicity of the N and acidity of the H in the methyl derivatives of pyridine and phenol. Domination by the intermolecular hydrogen bond between OH and N is the distinctive feature of association in 3-hydroxypyridines relative to association in phenol. The temperature dependence of _OH gives the enthalpy and entropy of association for 2, 4, 6-trimethyl-3-hydroxypyridine and of complex formation for various model systems. IR measurements confirm the conclusions.See [1] for the previous communication.We are indebted to G. G. Dvoryantseva for making the IR measurements.     

Intramolecular hydrogen bond in substituted 3-hydroxypyridines

To explain the character of the intramolecular hydrogen bond in substituted 3-hydroxypyridines, the chemical shifts in the NMR spectra of the hydroxyl group and the IR spectra were studied. It was established that the stability of the intramolecular hydrogen bond of the O-HNR₂ type in substituted 3-hydroxypyridines increases when compared with the corresponding phenols, while an opposite pattern is observed for bonds of the O-H0₂ N type. An approximate evaluation of the energy of the intramolecular hydrogen bond in substituted 3-hydroxypyridines was achieved. When reacting with bases of the same strength, 3-hydroxypyridine forms more stable complexes than phenol.     

IR spectra and structures of 3-hydroxyquinoline, 4-hydroxyisoquinoline,and their derivatives

From an examination of the frequencies, integral intensities, and half-widths of the absorption bands of the stretching vibrations of the hydroxyl groups in the IR spectra, it was concluded that 3-hydroxyquinoline, 4-hydroxyisoquinoline, and their derivatives exist in the phenol form in dilute CCl₄ solutions. Strong intermolecular hydrogen bonds, which are destroyed on dilution, exist in 3-hydroxyquinoline, 4-methyl-3-hydroxyquinoline, 4-hydroxyisoquinoline, and 1-chloro-3-methyl-4-hydroxyquinoline at concentrations above 10² M in CCl₄. From an examination of the values of halo derivatives of 3-hydroxyquinoline and 4-hydroxyisoquinoline, it was concluded that an intramolecular hydrogen bond of the OH...Hal type is present in these compounds. The shift in the OH band increases in the order Cl< Br< I. Weak bands of a free OH group that pertain to the s-trans form are observed in the spectrum. Strong intramolecular hydrogen bonds exist in 3-nitro-4-hydroxyisoquinoline and 3-piperidinomethyl-4-hydroxyisoquinoline.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1535–1539, November, 1971     

IR absorption spectra of 1-aryl-3-pyrazolidones

An examination of the frequencies and intensities of the valence vibration bands of carbonyl groups established that the phenyl group interacts with the C=O group of 1-phenyl-3-pyrazolidone and its m- and p-tolyl derivatives in solution. It is assumed that the interaction is accomplished through the N₁ and N₂ atoms in the sp² state. 1-Phenylpyrazolidone derivatives are strongly associated in CC1₄ and CHCl₃ solutions. The association decreases on passing from CCl₄ to CHCl₃ solutions and when there are methyl groups in the ortho positions of the phenyl rings. The energy of association between the 1-phenylpyrazolidones and organic bases (acetonitrile, ethyl acetate, and dioxane), evaluated from the shift in _nh, is 1.36–3.5 kcal/mole. The frequencies and integral intensities of the bands of the C=O and NH groups in chloroform were measured.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1678–1682, December, 1970.     

IR absorption spectra of a polyoxypropylenecarboranediol resin in the region ofν (OH) frequencies

Conclusions The IR spectra of CCl₄ solutions of polyoxypropylenecarboranediol resin in the region of the (OH) frequencies were studied. The hydroxyl groups participate in intra- and intermolecular hydrogen bands.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1857–1858, August, 1972.     

Molecular structures of some hydroxyazo compounds and their derivatives

The i.r. absorption spectra of 14 o-hydroxyazophenyl derivatives with increasing number of fused benzene rings of the aryl moiety are studied in solid state, in CCl₄ solution and in nujol mull. The i.r. spectral bands are assigned and indicate that these compounds exist in two tautomer forms. The OH group of the aryl moiety ortho to the azo group is responsible for the hydrazone structure. If solutions in CCl₄ are exposed to sunlight the strongly coloured compounds undergo a rapid bleaching, leading to a destruction of the azo group accompanied by an increase of hydrazone structures.     

Vibrational spectra and structure of some 3-hydroxypyridine 1-oxide derivatives

The vibrational spectra of 3-hydroxypyridine 1-oxide and its derivatives were investigated.On the basis of the assignments of the bands that characterize the OH, N⁺C⁺, and ring C-C bonds, it was established that these compounds exist in the crystalline state as associated zwitterions. It was shown that such associates have a more delocalized -electron system than the monomers.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 962–965, July, 1972.     

Effects of dipole interaction and solvation on the CO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the CO stretching (ν_CO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl₄ has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν_CO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν_CO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν_CO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl₄ solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν_CO band observed in a highly diluted CCl₄ solution (≤0.023 M) indicate that the solvation effect of CCl₄ is more complicated than those of cyclohexane and n-hexane. The analyses of the ν_CO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.     

Solvatochromism of Heteroaromatic Compounds: XXVII. Configuration Isomerism of H Complexes of Methanol with Carbonyl Compounds

The energy minimum of H complexes of methanol with carbonyl compounds corresponds to the nonlinear structure in which the bridging hydrogen atom deviates from the axis of the C=O bond. The stretching vibration bands of the OH bonds in these H complexes, observed in the IR spectra of solutions (CCl₄), have a complex shape or are asymmetrical, which is due to the existence of two configuration isomers differing in the direction of the H bond. Difference in the orientation of the subunits of the complex may cause significant differences in the OH stretching frequencies.     

Intramolecular hydrogen bonds and conformations of the 1,4-butanediol molecule

IR and Raman spectra of 1,4-butanediol (BD) versus variations in the medium (CCl₄, CH₃CN), concentration, temperature, and phase state were obtained. The observed changes attest to the conformational variety of BD molecules under the experimental conditions. On the basis of the analysis of the v(OH) region it is concluded that both in the gas phase and in CCl₄ solution conformers of BD with free OH groups coexist with conformers with O-H...O intramolecular hydrogen bonds. The difference in enthalpies, H, for the groups of conformers with and without intramolecular hydrogen bonds was found from the temperature dependence of the v(OH)_free and v(OH)_intra band intensities. The structures and energies for 70 possible spectrally and energetically distinguishable conformers of BD that do not take into account intramolecular hydrogen bonds were calculated by molecular mechanics with account of electron lone pairs of oxygen atoms. Using the experimental values of H and the calculated relative conformer energies,E, the intramolecular hydrogen bond energyE _intra= 3.7 kcal mol^–1 was found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1572–1577, September, 1993.     

In situ study of diffusion and interaction of water and electrolyte solution in polyacrylonitrile (PAN) membrane using FTIR and two-dimensional correlation analysis

In the study, the diffusion process of water and CaCl₂ aqueous solution in polyacrylonitrile (PAN) membrane have been investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and two-dimensional (2D) correlation analysis. In 2D ATR-FTIR spectra, the water ν(OH) band in PAN membrane during both water and CaCl₂ solution diffusion is split into three separate bands. However, the OH band appearing from bound water which forms hydrogen-bonding of CaCl₂ solution diffusion has a considerably lower wavenumber than that of pure water diffusion, which is due to association between Ca²⁺ ions and the CN groups in PAN. The sequential orders of the intensity changes for water and CaCl₂ solution diffusion in the region of ν(OH) and ν(CN) bands reveal the diffusion process and interaction of water and electrolyte in PAN membrane. That is, in the process of water diffusion in PAN membrane, water molecules first interact with –CN group in PAN to form weak hydrogen bond, then the moderate hydrogen-bonding interactions start gradually, and finally, the strong hydrogen-bonding interactions may be formed. When CaCl₂ solution diffuses in PAN membrane, the CN groups in PAN first associate with Ca²⁺ ions and then interact with water molecules to form hydrogen bond that grows gradually from weak to strong. Furthermore, the results are validated further by band fitting to calculate the ratio of each component band area and the proportion of component band to ν(OH) water band.     

INTRAMOLECULAR OH···S HYDROGEN BONDS AND MOLECULAR CONFORMATIONS IN 2-METHYLMERCAPTOETHANOL

Abstract

The infrared absorption spectrum of monomeric 2-methylmercaptoethanol in dilute CC1₄, solution exhibits four overlapped bands in the fundamental OH stretching region. The individual band components were resolved using digital computing techniques [1], and the relative band intensities are temperature dependent. The “free” OH bands at 3634 and 3623 cm correspond to gauche and trans orientations about the C-O bond, respectively, by analogy with similar band components in the infrared spectrum of ethanol in dilute CC1₄, solution. The OH bands at 3539 and 3446 cm^?1 are assigned to gGt and gGg¹ conformers, respectively, each involving an intramolecular OH···S hydrogen bond (conformer notation refers to the orientation about the C-O, C-C and C-S(CH₃) bonds, respectively). A similar interpretation of the matrix isolated infrared spectra of ethylene glycol, involving two conformers with intramolecular OH···O hydrogen bonds and differing principally in the orientation of the proton-acceptor OH group, has been presented recently [2]. The microwave spectrum of 2-mercaptoethanol in the vapour phase arises from an all-gauche conformation with an intramolecular OH···S hydrogen bond [3].     

Raman Spectroscopic Study of Aluminum Silicate Complexes at 20°C in Basic Solutions

Raman spectroscopic measurements were performed at ambient temperature onaqueous silica-bearing solutions (0.005 < m _Si < 0.02; 0 < pH < 14). The spectraare consistent with the formation of monomeric Si(OH)^o ₄, SiO(OH)^– ₃ andSiO₂(OH)^2– ₂ species at acid to neutral, basic, and strongly basic pH, respectively.Raman spectra of aqueous Al-bearing solutions at basic pH confirm thepredominance of the Al(OH)^– ₄ species in a wide concentration range (0.01 < m _Al < 0.1).Raman spectra of basic solutions (12.4 < pH < 14.3), containing both Al andSi, exhibit a strong decrease in intensities of SiO(OH)^– ₃, SiO₂(OH)^2– ₂, andAl(OH)^– ₄ bands in comparison with Al-free Si-bearing and Si-free Al-bearingsolutions of the same metal concentration and pH, suggesting the formation ofsoluble Al—Si complexes. The amounts of complexed Al and Si derived fromthe measurements of the Al and Si band intensities in strongly basic solutions(pH 14) are consistent with the formation, between Al(OH)^– ₄ andSiO₂(OH)^2– ₂, of the single Al—Si dimer SiAlO₃(OH)^3– ₄ according to the reactionSiO₂(OH)^2– ₂ + Al(OH)^– ₄ SiAlO₃(OH)^3– ₄ + H₂OAt lower pH ( 12.5) the changes in band intensities are consistent with theformation of several, likely more polymerized, Al—Si complexes.     

Molecular structure and IR absorption spectra of perfluorinated aldehyde hydrates (n-CxF2x+1CH(OH)2, x = 1-4)

Structures and IR absorption spectra of the conformational isomers of perfluorinated aldehyde hydrates, n-C_xF_2x+1CH(OH)₂, (x = 1-4) have been calculated using density functional theory (DFT) and compared to experimental FT-IR measurements. Two absorption peaks around 3600-3700 cm⁻¹ were observed and are assigned to OH stretching modes of OH groups with, and without, intramolecular hydrogen bonding. For n-C₃F₇CH(OH)₂, two absorption bands around 900-1000 cm⁻¹ were observed in the experimental spectra, whereas only a single in-phase stretching mode of the (CF₃)(C₂F₄CH(OH)₂) and (C₃F₇)(CH(OH)₂) bonds was calculated for each conformer. The experimental spectra were well described by composite spectra of the thermal equilibrium mixture of different conformational isomers of n-C_xF_2x+1CH(OH)₂ calculated by DFT.     

Quantum chemical study of several monocyclic complex β‐lactam C‐3, C‐4, and N‐derivatives,and β‐ring model molecules

A quantum chemical study of several complex monocyclic 4‐benzoyl‐4‐phenyl‐β‐lactam derivatives was carried out using cyclobutane, azetidine, 2‐azetidinone, 1‐methyl‐2‐azetidinone, and 3‐methyl‐2‐azetidinone as model compounds. The optimum geometry was obtained for the different conformations. The planarity of the ring was discussed in terms of the influence of the substituents on the amide resonance. To better analyze the amide resonance and the activity of the β‐lactam ring, a vibrational study was also carried out. To examine the influence of solvent polarity on the carbonyl bands, the Fourier transform–infrared (FT‐IR) spectra of the β‐lactam monocyclic derivatives were recorded in CCl₄, C₆H₆, and CHCl₃ solutions. The normal vibrations of the β‐lactam ring in the model compounds were characterized and used in the analysis of the β‐ring of more complex derivatives. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Reactions of alkoxy and hydroxy radicals generated photochemically from hydroperoxide molecules

In the present work as well as HRO^. radicals were generated in the photochemical interaction of 1,2-benzanthracene with -ethyl phenyl hydroperoxide /HROOH/ in C₆H₆ and CCl₄ at 304 K. radicals were trapped by C₆H₆. The main reaction of HRO^. radicals is hydrogen abstraction from the hydroperoxide group of HROOH. Although OH radicals are less selective, the hydrogen abstraction is the main process during their interaction with aromatics in contrast to reactions in aqueous solutions, where addition to the benzene ring is the rate-determining process in CCl₄:

Synthesis and physical–chemical properties of hydrolyzed nanosized mesoporous fluorocarbon materials and carbon–fluorocarbon composites

Hydrolysis of nanosized mesoporous superstoichiometric fluorocarbon material FS (CF_{1.20 ± 0.03}) and carbon–fluorocarbon nanocomposites NCFC (CF_{0.93 ± 0.03}) by 10% KOH in aqueous-alcohol solution was studied and yielded two new classes of the hydrolyzed fluorocarbon nanomaterials: hydroxofluorocarbon nano-material FS–OH of general formula sp³-C_1−yF_n−x(OH)_x (n = 1; x > 0.1, y ∼ 0.05–0.1) and carbon–hydroxofluorocarbon nanocomposites NCFC–OH of general formula sp²-C_m*sp³-C_1−yF_n−x(OH)_x (n = 1; x ∼ 0; y ∼ 0.1–0.2).FTIR and Raman studies of FS–OH and NCFC–OH materials have shown that hydrolysis of sp³-C–F-bonds in these materials leads a decrease of sp³-C–F amount and appearance of characteristic absorption bands for sp³-C–OHO, carboxyls and carbonyls, typical for oxidized graphites, carbon blacks and various soots. These phenomena, in combination with C,H,F-analyses for FS–OH and NCFC–OH products have allowed to state that hydrolysis of FS and NCFC in KOH solutions can be explained by the substitution reactions of surface sp³-C–F to sp³-C–OH and sp²>CO containing groups.Observed hydrolytic reactions are also accompanied with processes of the colored solutions origin (yellow – for FS and red-brown – for NCFC). These solutions have UV-VIS spectra identical to graphene oxide and graphitic acid.     

The kinetics of radiation-induced hydrogen abstraction by CCl3 radicals in the liquid phase: Cyclohexene

The kinetics of hydrogen abstraction from cyclohexene by CCl₃ radicals were studied in CCl₄ solution as a function of cyclohexene concentration and temperature in the range of 26–140°C. The CCl₃ radicals were produced both by radiolysis of CCl₄ and by photolysis of CCl₃Br. The rate constant for the reaction was found to be given by the equation where θ = 2.303 RT kcal/mol. This activation energy leads to C? H bond strength for the allylic hydrogen of 85 ± 1 kcal/mol, which means a resonance stabilization energy of 11 ± 1.5 kcal/mol for the C-C₆H₁₁ radical.     

The torsional barrier in aromatic carbonyl compounds. VI. Carbon-13 and 1H DNMR study of protonated alkyl and haloalkyl p-tolyl ketones

The free energy of activation of the torsional barrier around the phenyl–carbonyl bond in a series of stable protonated α-substituted p-methylacetophenones (p-tolyl- where R = CH₃, C₂H₅, i-C₃H₇, t-C₄H₉, CH₂Cl, CHCl₂, CCl₃, CH₂F, CHF₂, CF₃ and CH₂Br) has been evaluated by complete lineshape analysis of ¹³C or proton low temperature NMR spectra. α-Substitution by an alkyl group leads to a decrease of the barrier height due to both steric and electronic effects. For the halo compounds, steric and electronic effects of the substituents are in competition, leading to a very high ΔG^≠ value in protonated α,α,α-trifluoro-p-methylacetophenone (63.2 kJ mol^?1). In addition, the twist angle of the protonated carbonyl group has been tentatively evaluated by the use of the (modified) Stothers's method.