Molecular interaction studies in hydrogen bonded polar binary mixtures

The molecular interactions between the polar systems of propan-1-ol (1PN) with alkyl benzoates (methyl benzoate and ethyl benzoate) for various mole fractions at different temperatures are studied by determining the dielectric permittivity in radio, microwave and optic frequency regions, respectively. Dipole moment, excess dipole moment, excess Helmholtz free energy, excess permittivity, relaxation time, excess inverse relaxation time and excess thermodynamical values are calculated using experimental data. Hamiltonian quantum mechanical calculations are performed on both pure and equimolar binary systems of 1PN with alkyl benzoates for the measurement of dipole moment from the ab initio Hartree–Fock and density functional theory (B3LYP) methods with 6-31?+?G* and 6-311?+?G** basis sets using Spartan 08 modelling software and these theoretical values are in good agreement with the experimental values.     

Evaluation of dipole moment of hydrogen bonded complexes of long-chain alcohols with acetic acid and chlorobenzene

The formation of 1 : 1 complexes involving n-pentanol-acetic acid, n-hexanol-chlorobenzene and n-heptanol-chlorobenzene in a non-polar solvent tetrachlormethane have been studied at the frequency of 455 kHz and at the temperature of 303.16 K. The dipole moment of 1 : 1 complex μ _ab , molar polarisation P_ab , and interaction dipole moment Δμ in all these ternary mixtures have been evaluated. The results indicate that complexation is due to polarisation effect.     

Development of eclipsed and staggered forms in some hydrogen bonded complexes

Intermolecular hydrogen bonding in X₃CH···NH₃ (X = H, F, Cl, and Br) complexes has been studied by B3LYP, B3PW91, MP2, MP3, MP4, and CCSD methods using 6‐311++G(d,p) and AUG‐cc‐PVTZ basis sets. These complexes could exist in both eclipsed (EC) and staggered (ST) forms. The differences between binding energies of EC and ST forms are negligible and all EC and ST shapes correspond to minimum stationary states. The order of stabilities of them is in an agreement with the results of atoms in molecules (AIM) and natural bond orbital (NBO) analyses. On the basis of low differences between binding energies, ST forms are more stable than EC forms in all complexes with the exception of Br₃CH···NH₃, which behaves just opposite. Although the differences between binding energies are negligible, they are consistent with the results of AIM analysis. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Theoretical study of hydrogen bonded complexes of dimethyl disulfide or dimethyl peroxide with nitric acid

Ab initio and DFT calculations performed on the title systems revealed two types of structures for both DMDS-HNO₃ and DMDO-HNO₃ complexes. In both structures two hydrogen bonds are formed between the OH group interacting with one of sulfur (or oxygen) atoms and methyl CH group being a proton donor to one of the oxygen atoms of the NO₂ group of nitric acid. Depending on the location of the interacting methyl group with respect to the S or O acceptor of the main O-H?S(O) bond, the seven or eight-membered ring structures are formed. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed for the proton donor molecule. The calculated binding energies are between −20.86 and −29.95 kJ/mol at MP2 and between −17.52 and −27.47 kJ/mol at B3LYP using the 6-311++G(2d,2p) basis set. The complexes involving disulfide are slightly weaker by ca. 6.7-8.6 kJ/mol than the corresponding peroxide complexes. The performed NBO analysis reveals that the charge transferred to σ*(OH) orbital of the nitric acid molecule comes mainly from the high p-character lone pair orbital of sulfur or oxygen atom being the hydrogen bond acceptor site in the disulfide or peroxide molecule.     

Vibrational analysis of free and hydrogen bonded complexes of nicotinamide and picolinamide

Harmonic and anharmonic vibrations of free nicotinamide (NIA) and picolinamide (PIA) molecules together with their hydrogen bonded complexes H₂O–NIA and H₂O–PIA have been studied by means of density functional method. The calculation results of the vibrational spectra of free molecules have been investigated and are compared to the available experimental spectra. The vibrational wavenumbers of both molecules have also been calculated by polarizable continuum model (PCM) that represents the solvent as a polarizable continuum and places the solute in a cavity within the solvent (water is chosen as the solvent in this study). The results of PCM calculations and the H₂O–NIA, H₂O–PIA complexes, are used to investigate the H-bonding interactions of both molecules with the water molecule. The harmonic wavenumbers have been scaled by proper factors obtained by comparing the observed versus calculated wavenumbers and it is shown that anharmonic corrections on the vibrational spectra provided a better agreement between the observed and calculated wavenumbers compared to the results obtained by scaling factor method.     

Geometrical features of hydrogen bonded complexes involving sterically hindered pyridines

The ability of strongly sterically hindered pyridines to form hydrogen bonded complexes was inspected using low-temperature 1H and 15N NMR spectroscopy in a liquefied Freon mixture. The proton acceptors were 2,6-di(tert-butyl)-4-methyl- and 2,6-di(tert-butyl)-4-diethylaminopyridine; the proton donors were hydrogen tetrafluoroborate, hydrogen chloride, and hydrogen fluoride. The presence of the tert-butyl groups in the ortho positions dramatically perturbed the geometry of the forming hydrogen bonds. As revealed by experiment, the studied crowded pyridines could form hydrogen bonded complexes with proton donors exclusively through their protonation. Even the strongest small proton acceptor, anion F-, could not be received by the protonated base. Instead, the simplest hydrogen bonded complex involved the [FHF]- anion. This complex was characterized by the shortest possible N...F distance of about 2.8 A. Because the ortho tert-butyl groups did not prevent the hydrogen bond interaction between the protonated center and the anion completely, an increase of the pyridine basicity caused a further shortening of the N-H distance and a weakening of the hydrogen bond to the counterion.     

Thermal analysis of hydrogen bonded benzoic acid liquid crystals

Novel homologous series of supramolecular hydrogen bonded liquid crystals have been investigated. Hydrogen bonds are formed between p-n octyloxy benzoic acid and various p-n alkyloxy benzoic acids whose carbon chain length varied from pentyl to dodecyl. These complexes are characterized by Fourier transform infrared spectroscopy, polarizing optical microscopy (POM), and differential scanning calorimetry (DSC). Phase diagram is constructed from POM and DSC data. The order of the phase transitions is determined by Navard and Cox ratio (N _R). Characteristic phases like nematic, smectic C, and smectic F are identified. A new smectic ordering observed in this series is investigated by constructing phase diagram obtained from two binary mixtures of the present homologs. Inter-digitation of lamellar layers is observed to be one of the reasons for the occurrence of new smectic ordering. Optical tilt angle in smectic C phase is fitted to a power law. The magnitude of exponent of the power law is found to concur with the Mean Field theory predicted value.     

Thermal solid state synthesis of coordination complexes from hydrogen bonded precursors

Thermal dehydrochlorination of crystalline 4-picolinium salts of [PtCl4]2- and [PdCl4]2- leads to formation of trans-[MCl2(4-picoline)2](M = Pt, Pd).     

Theoretical study of hydrogen bonded clusters of water and fulminic acid

Ab initio and density functional calculations are used to analyze the interaction between a molecule of fulminic acid with 1, 2, 3, and 4 molecules of water along with a 2:2 complex at B3LYP/6-31+G(d,p) and MP2/6-311++G(d,p) computational levels. Cooperative effect (CE) in terms of stabilization energy of clusters are calculated and discussed as well. CE is increased with increasing cluster size of studied clusters. Red shifts of H–C stretching frequency for complexes involving HCNO as H-donor are predicted.     

Nuclear hyperfine interaction of rotating hydrogen: a spectroscopic investigation of hydrogen-OCS van der Waals complexes

The rotational spectra of five weakly bonded hydrogen-OCS complexes (paraH(2), orthoH(2), HD, orthoD(2), and paraD(2)) are measured. Hyperfine structure is resolved and analyzed in all except the complex with paraH(2), where I=0. For the two j=1 species, orthoH(2)-OCS and paraD(2)-OCS, nuclear hyperfine coupling constants are found to be d(a)=21.2(2) and 8.4(2) kHz, respectively, indicative of nearly free uniaxial rotation of the hydrogen around the b-inertial axis. Similar analyses for HD-OCS and orthoD(2)-OCS yield the quadrupole coupling constants eqQ(a)=16(2) and 30(2) kHz, respectively, showing that the internal rotational motions of HD and orthoD(2) in the complex are slightly hindered producing a small nonspherical distribution. For orthoD(2)-OCS, the observed hyperfine structure indicates that the nuclear spin states I=0 and 2 are strongly coupled in the rotation of the complex.     

Pyroelectric investigations of a hydrogen bonded ferroelectric liquid crystal gel by LIMM

The laser intensity modulation method (LIMM) is employed to determine spatially resolved polarization distributions in sandwich cells containing a hydrogen‐bonded ferroelectric liquid crystal (FLC) gel. At no external electric fields, contributions to the distributions at the surface of the FLC layer are dominating in all the samples with different concentration of gel former. These are attributed to non‐vanishing polarization due to surface interaction. In this case, the effect of hydrogen‐bonded network on the polarization distribution is not visible. In external electric fields, additional contribution to the resulting distribution caused by the induced polarization due to unwinding the FLC helix has been observed. Furthermore, the influence of hydrogen‐bonded network on the polarization distribution is also detected when the gel former content is increased up to 5.0 wt%. Therein the shape of the measured pyrospectra is completely different to other FLC gel samples with lower gel former concentration, where their maximum distributions still locate at the surface of FLC layer which is comparable to the initial field‐free state. These result indicate that the helical structure and orientation director of FLC are able to be stabilized effectively by the gel network even under strong external electric field. Copyright © 2004 John Wiley & Sons, Ltd.     

Boronic acid hydrogen bonding in encapsulation complexes

Hydrogen bonding is a key determinant of much macromolecular structure in nature, but individual donor and acceptor pairs are rarely observed in solution. Their weak interactions result in nanosecond lifetimes and rapid exchange of partners. Reversible encapsulation isolates molecules in very small spaces for milliseconds to hours and allows their characterization by NMR methods. Here we report a competitive study of hydrogen-bonding functions--carboxylic acids, primary amides, and boronic acids--within a multicomponent capsular assembly. The pairwise co-encapsulation of these molecules allows the direct observation of homodimeric boronic acids and their heterodimeric complexes with carboxylic acids and primary amides. The efficiency of boronic acids as hydrogen-bonding partners derives from their adaptable structures rather than from their intrinsic acid/base properties.     

On the mechanism of proton transfer reactions in the excited hydrogen bonded complexes

The results of systematic experimental studies on the hydrogen bonding and proton transfer reactions between excited naphthol molecule and aliphatic amine molecule in nonhydroxylic solvents are described and interpreted.The mechanism of the proton transfer process is discussed on the basis of the - interaction in the hydroxy group of naphthol and the charge transfer interaction between the proton acceptor and the donor in the excited electronic state.

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Zusammenfassung Die Ergebnisse systematischer experimenteller Untersuchungen über Wasserstoffbrückenbindung und Protonenaustausch zwischen angeregten Naphtholmolekülen und aliphatischen Aminen werden beschrieben und interpretiert. Es werden Lösungsmittel ohne Hydroxylgruppen benutzt.Der Mechanismus der Protonenaustauschreaktion wird diskutiert auf der Basis einer --Wechselwirkung in der Hydroxylgruppe des Naphtholmoleküls und einer charge-transfer-Wechselwirkung zwischen Protonen-Akzeptor und -Donor. Dabei befindet sich der Donor in einem angeregten Elektronenzustand.

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Résumé Les résultats d'études systématiques expérimentales sur la liaison hydrogène et les réactions de transfert de proton entre des molécules de naphtol excitées et des amines aliphatiques sont décrits et interprétés. Des solvants non-hydroxyliques sont employés.Le mécanisme du transfert de proton est discuté sur base d'une interréaction - dans la groupe hydroxyle du naphtol et d'un transfert de charge entre l'accepteur et le donneur du proton, le donneur étant en état excité.

     

The low frequency vibrations of hydrogen bonded adipic acid crystals

The low frequency vibrational spectrum of crystalline adipic acid has been investigated in the range 20–450 cm⁻¹ at room and low temperatures. The experimental results are compared to ab initio results on a model asymmetric unit. It is shown that the doublet and quartet structures observed for several bands are due to Davydov splitting and Fermi resonance effects.     

Structure and properties of hydrogen bonded complexes of pyridine-N-oxide and its derivatives

Molar Kerr constants and electric dipole moments of hydrogen bonded complexes that pyridine-N-oxide and its derivatives form with phenols are studied (a) experimentally, (b) by the vector/tensor addition scheme, and (c) by AM1 and PM3 semi-empirical quantum chemical methods. The data are used to establish the geometry of the complexes. It is shown that for a series of pyridine-N-oxide derivatives, the logarithm of the complex formation equilibrium constant correlates with the charge on the oxygen atom of the N–O group. A method to calculate the first and second complex formation constants based on the electric properties of the individual components of the complex is proposed. A relationship between the polarity of the hydrogen bond and the sum of the charges on the hydrogen and oxygen atoms forming the bond is established for the complexes under study.     

Electrically caused vibrational frequency shifts and dipole moments in rare gas hydrogen bonded complexes

The Liu-Dykstra theory of electrical influence on vibrational potentials in hydrogen bonded complexes is shown to account very well for vibrational frequency shifts and induced dipoles in a series of rare gas complexes with hydrogen fluoride. The behavior of the electrical interaction energy and dipole moment are shown in detail for Ar-HF.     

Hydrogen bonded complexes of cyanuric acid with pyridine and guanidinium carbonate

Hydrogen bonded complexes of cyanuric acid (CA) with pyridine, [C₃N₃H₃O₃:C₅H₅N], 1, and guanidinium carbonate [C₃H₂N₃][C(NH₂)₃],2, have been prepared at room temperature and characterized by single-crystal X-ray diffraction. Structure of 1 shows pyridine molecules substituting the inter-tape hydrogen bond in CA by N-H… N and C-H…O hydrogen bonds. The structure reveals CA-pyridine hydrogen-bonded single helices held together by dimeric N-H…O hydrogen bonding between CA molecules. In2, the CA tapes, resembling a sine wave interact with the guanidinium cations through N-H…O and N-H…N hydrogen bonds forming guanidinium cyanurate sheets.     

Enthalpy of hydrogen bonded alcohol-butyl amine complexes by a simpler calorimetric method

The heats of mixing ofn-butyl amine with methanol andn-propanol have been determined at 30° C and the enthalpies of alcohol-amine complex formation have been calculated by thermochemical cycle. The enthalpies of complex formation of butyl amine with methanol andn-propanol were found to be-44.3 kJ/mole and-39.4 kj/mole respectively. The heats of mixing of synthetically prepared 1:1 molar mixtures of n-butyl amine with methanol, ethanol andn-propanol withn-hexane have also been determined at 30° C. The enthalpy of amine-alcohol complexes was obtained from the partial molar heats of dissociation of the complexes inn-hexane. The values agree with those obtained by the thermochemical cycle method. NCL Communication No. 2561.