Effects Of Molecular Association Research Articles

Investigation of intermolecular hydrogen bonding in 2,3,4,5,6 pentafluorobenzoic acid through molecular structure and vibrational analysis – A DFT approach

The density functional theory (DFT) and Hatree–Fock (HF) method was performed at 6-311++G∗∗ level to derive the equilibrium geometry, vibrational wavenumbers, infrared intensities and Raman scattering activities of 2,3,4,5,6 pentafluorobenzoic acid molecule (PFBA). The conformer study of the monomer PFBA was also undertaken. The possibility of intermolecular hydrogen bonding and the dimeric form of the molecule was predicted using vibrational analysis of the monomer. The effects of molecular association through OH⋯O hydrogen bonding have been described in the dimer structure using geometrical structure analysis, natural bond orbital analysis (NBO), molecular electrostatic potential (MEP) maps and Mulliken charge analysis.

Monomeric and dimeric structures analysis and spectroscopic characterization of 3,5-difluorophenylboronic acid with experimental (FT-IR, FT-Raman, 1H and 13C NMR, UV) techniques and quantum chemical calculations

The spectroscopic properties of 3,5-difluorophenylboronic acid (3,5-DFPBA, C6H3F2B(OH)2) were investigated by FT-IR, FT-Raman UV–Vis, 1H and 13C NMR spectroscopic techniques. FT-IR (4000–400cm–1) and FT-Raman spectra (3500–10cm–1) in the solid phase and 1H and 13C NMR spectra in DMSO solution were recorded. The UV spectra that dissolved in ethanol and water were recorded in the range of 200–400nm for each solution. The structural and spectroscopic data of the molecule have been obtained for possible three conformers from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. Hydrogen-bonded dimer of title molecule, optimized by counterpoise correction, was also studied B3LYP at the 6-311++G(d,p) level and the effects of molecular association through O–H⋯O hydrogen bonding have been discussed. 1H and 13C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, were performed by time-dependent density functional theory (TD-DFT) results complements with the experimental findings. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (OPDOS) diagrams analysis were presented. The effects due to the substitutions of boric acid group and halogen were investigated. The results of the calculations were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), nonlinear optical properties (NLO) and thermodynamic features were performed.

Quantum-chemical (DFT, MP2) and spectroscopic studies (FT-IR and UV) of monomeric and dimeric structures of 2(3H)-Benzothiazolone

Molecular geometry and vibrational wavenumbers of 2(3H)-Benzothiazolone (C7H5NSO, HBT) was investigated using density functional (DFT/B3LYP) method with 6-311+G(d,p) basis set. The vibrational wavenumbers are found to be in good agreement with experimental FT-IR spectra. Hydrogen-bonded dimer of HBT, optimized by counterpoise correction, was studied by MP2 and DFT/B3LYP at the 6-311+G(d,p) level and the effects of molecular association through NH---O hydrogen bonding were discussed. A detailed analysis of the nature of the hydrogen bonding, using topological parameters, such as electronic charge density, Laplacian, kinetic and potential energy density evaluated at bond critical points (BCP) has also been presented. The UV absorption spectra of the compound dissolved in ethanol and chloroform solutions were recorded in the range of 200–600nm. The UV–vis spectrum of the title molecule was also calculated using TD-DFT method. The calculated energy and oscillator strength almost exactly reproduce the experimental data. Total and partial density of state (TDOS, PDOS) of the HBT in terms of HOMOs and LUMOs and molecular electrostatic potential (MEP) were calculated and analyzed. The electric dipole moment, polarizability and the first static hyper-polarizability values for HBT were calculated at the DFT/B3LYP with 6-311+G(d,p) basis set. The results also show that the HBT molecule may have nonlinear optical (NLO) comportment with non-zero values. Stability of the molecule arising from hyper-conjugative interactions and charge delocalization was analyzed using natural bond orbital (NBO) analysis.

An experimental and theoretical investigation of Acenaphthene-5-boronic acid: Conformational study, NBO and NLO analysis, molecular structure and FT-IR, FT-Raman, NMR and UV spectra

The solid state Fourier transform infrared (FT-IR) and FT-Raman spectra of Acenaphthene-5-boronic acid (AN-5-BA), have been recorded in the range 4000–400cm−1 and 4000–10cm−1, respectively. Density functional theory (DFT), with the B3LYP functional was used for the optimization of the ground state geometry and simulation of the infrared and Raman spectra of the molecule. The vibrational wave numbers and their assignments were examined theoretically using the Gaussian 09 set of quantum chemistry codes and the normal modes were assigned by a scaled quantum mechanical (SQM) force field approach. Hydrogen-bonded dimer of AN-5-BA, optimized by counterpoise correction, has also been studied by B3LYP at the 6-311++G(d,p) level and the effects of molecular association through O–H⋯O hydrogen bonding have been discussed. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by Gauge-Including Atomic Orbital (GIAO) method. Natural bond orbital (NBO) analysis has been applied to study stability of the molecule arising from charge delocalization. UV spectrum of the title compound was also recorded and the electronic properties, such as frontier orbitals, and band gap energies were measured by TD-DFT approach. The first order hyperpolarizability 〈β〉, its components and associated properties such as average polarizability and anisotropy of the polarizability (α and Δα) of AN-5-BA was calculated using the finite-field approach.

Molecular structure, spectroscopic (FT-IR, FT-Raman), NBO and HOMO–LUMO analyses, computation of thermodynamic functions for various temperatures of 2, 6-dichloro-3-nitrobenzoic acid

The FT-IR and Raman spectra of 2, 6-dichloro-3-nitrobenzoic acid (DCNBA) have been recorded and analyzed. The equilibrium geometry, various bonding and harmonic vibrational wavenumbers have been calculated with the help of density functional theory (DFT/B3LYP/cc-pvdz/6-311++G(d,p)) method. The optimized geometrical parameters obtained by B3LYP/6-311++G(d,p) method show good agreement with experimental X-ray data. Most of the vibrational modes are observed in the expected range. The Mulliken population analysis shows the interactions of CNO⋯HC and CO⋯HC. The most possible interaction is explained using natural bond orbital (NBO) analysis. The effects of molecular association through OH⋯O hydrogen bonding have been described by the single dimer structure. The strengthening and polarization of the CO bond increases due to the degree of conjugation. HOMO–LUMO energy and the thermodynamic parameters are also evaluated. The thermodynamic functions (heat capacity, internal heat energy, Gibbs energy and entropy) from spectroscopic data by statistical methods were obtained for the range of temperature 100–1000K.

Monomeric and dimeric structures, electronic properties and vibrational spectra of azelaic acid by HF and B3LYP methods

Quantum chemical calculations of energies, dipole moment, polarizability, hyperpolarizability and vibrational wavenumbers of Azelaic acid (AZA) were carried out by using ab initio HF and B3LYP methods with 6-311++G(d,p) basis set. Hydrogen-bonded dimer of AZA, optimized by counterpoise correction, has also been studied by HF and B3LYP at the 6-311++G(d,p) level and the effects of molecular association through OH⋯O hydrogen bonding have been discussed. A complete vibrational analysis of AZA has been performed and assignments are made on the basis of potential energy distribution. The comparisons and assignments of the vibrational frequencies indicate that the experimental spectra also correspond acceptably with those of theoretically simulated spectra except the hydrogen-bonded coupled infrared vibrations.

Spectroscopic (FTIR, FT-Raman, NMR and UV) and molecular structure investigations of 1,5-diphenylpenta-1,4-dien-3-one: A combined experimental and theoretical study

Fourier transform infrared (FTIR) and FT-Raman spectra have been recorded and extensive spectroscopic investigations have been carried out on 1,5-diphenylpenta-1,4-dien-3-one [dibenzalacetone (DBA)]. The effects of molecular association through CH⋯O hydrogen bonding have been described by the single dimer structure. The optimized geometries, wavenumber and intensity of the vibrational bands of dibenzal acetone have been calculated using density functional theory (DFT) employing B3LYP functional and 6-31G(d,p) basis set. On the basis of the comparison between calculated and experimental results assignments of the fundamental vibrational modes are examined. 13C and 1H NMR spectra have been recorded and 13C and 1H nuclear magnetic resonance chemical shifts of the molecule have been calculated using the gauge independent atomic orbital (GIAO) method. The molecular stability and bond strength have been investigated by applying the Natural Bond Orbital analysis (NBO). The electronic properties like UV spectral analysis and HOMO–LUMO analysis of DBA have been reported. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with molecular electrostatic potential (MEP).

A New Modified van Laar Model for Associating Mixtures

In this study, a modification is presented for van Laar model (van der Waals mixture theory) for association mixtures. The molecular association effects are considered in van der Waals mixture theory by adding two new steps to van Laar cycle. The excess Gibbs free energy function and corresponding activity coefficient equations are derived for presented model. In addition to general case when both components are associating fluids, model simplified for two interesting cases: (i) only one fluid is associating, (ii) two fluids are associating but only self-associated species exist in the mixture. This model also is used for VLE calculations for 16 different binary mixtures in which one or both components are associating fluids. Results of the presented model show satisfactory improvement over the nonassociating case for vapor liquid equilibrium (VLE) prediction.

Molecular structure, spectroscopic (FTIR, FTIR gas phase, FT‐Raman) first‐order hyperpolarizability and HOMO–LUMO analysis of 4‐methoxy‐2‐methyl benzoic acid

AbstractVibrational spectral analysis was carried out for 4‐methoxy‐2‐methyl benzoic acid (4M2MBA) by using Fourier transform infrared (FT‐IR) (solid, gas phase) and FT‐Raman spectroscopy in the range of 400–4000 and 10–3500 cm−1 respectively. The effects of molecular association through OH···O hydrogen bonding have been described by the single dimer structure. The theoretical computational density functional theory (DFT) and Hatree‐Fock (HF) method were performed at 6–311++G(d,p) levels to derive the equilibrium geometry, vibrational wavenumbers, infrared intensities and Raman scattering activities. The scaled theoretical wavenumbers were also shown to be in good agreement with experimental data. The first‐order hyperpolarizability (β0) of this novel molecular system and related properties (β, α0 and Δα) of 4M2MBA are calculated using the B3LYP/cc‐pvdz basis set, based on the finite‐field approach. A detailed interpretation of the infrared and Raman spectra of 4M2MBA is reported. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule were also constructed and compared with the experimental one. Copyright © 2010 John Wiley & Sons, Ltd.

Effect of hydrogen bonding in the vibrational spectra of trans‐cinnamic acid

AbstractA computationally‐assisted methodology to assign the vibrational spectra of molecular materials (PiMM) has been successfully applied to the Raman and infrared (IR) spectra of trans‐cinnamic acid (t‐CIA) in the solid state. The effects of molecular association through OH···O hydrogen‐bonding in both the wavenumber and the intensity of the bands are accurately described by a single dimer structure. This supports the discrimination between the possible conformers in the solid, the complete evaluation of hydrogen‐bonding effects, and the full assignment of the vibrational spectra of t‐CIA. Copyright © 2008 John Wiley & Sons, Ltd.

Effects of Molecular Association on Polarizability Relaxation in Liquid Mixtures of Benzene and Hexafluorobenzene

In this work we have studied the relaxation dynamics of the many-body polarizability anisotropy in liquid mixtures of benzene (Bz) and hexafluorobenzene (Hf) at room temperature by femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) experiments and molecular dynamics (MD) simulations. The computed polarizability response arising from intermolecular interactions was included using the first-order dipole-induced-dipole model with the molecular polarizability distributed over the carbon sites of each molecule. We found good qualitative agreement between experiments and simulations in the features exhibited by the nuclear response function R(t) for pure liquids and mixtures. The long-time diffusive decay of R(t) was observed to vary substantially with composition, slowing down noticeably with dilution of each of the species as compared with that in the corresponding pure liquids. MD simulation shows that the effect on R(t) is due to the formation of strong and localized intermolecular association between Bz and Hf species that hinder the rotational diffusive dynamics. The formation of these Bz-Hf complexes in the liquid mixtures also modifies the rotational diffusive dynamics of the component species in such a way that cannot be explained solely in terms of a viscosity effect. Even though the computed orientational diffusive relaxation times associated with Bz and Hf are larger by a factor of approximately 2 than those from experiments, we found similar trends in experiments and simulations for these characteristic times as a function of composition. Namely, the collective and single-molecule orientational correlation times associated with Bz are observed to grow monotonically with the dilution of Bz, while those corresponding to Hf species exhibit a maximum at the equimolar composition. We attribute the quantitative discrepancy between experiments and simulations to the use of the Williams potential, which seems to overestimate the intermolecular interactions and thus predicts not only a slower translational dynamics but also a slower rotational diffusion dynamics than in real fluids.

The influence of association of alcohol molecules on their adsorption and desorption heats

The paper presents the results of calorimetric measurements and surface excess adsorption isotherms for adsorption process of n-butanol from n-hexane on controlled porosity glasses of different mean pore diameters. The pore diameter was found to have very small effect on the adsorption heat, while it affects the desorption heat recorded by the flow microcalorimeter. Moreover, in the region of very low alcohol concentration in solution, the heat of adsorption exhibits sharp maximum for both narrow and wide pore diameters. This rather puzzling result is attributed to the effect of molecular association of alcohol molecules in the solution.

Phase behavior of lattice associating binary mixtures: a Monte Carlo study.

The lattice gas model is used to study effects of molecular association on the phase behavior of binary symmetric mixtures, in which only dimers consisting of different particles can form. It is demonstrated that the increase of the association energy leads to qualitative changes of the phase diagrams. In particular, the demixing transition is observed only for sufficiently low association energy. That demixing transition can be either first order or continuous. For sufficiently high energy of association the condensed phase shows a very well ordered structure even at high temperatures.

Effect of molecular association and reactivity on substitution in chromium(III)-salprn complexes

A new chromium(III)-Schiff base complex, [Cr(5-chlorosalprn)(H2O)(2)]ClO4, where salprn=N,N'-propylenebis(salicylideneimine) has been prepared and characterized by electrospray ionization mass spectrometric (ESIMS) analysis and other spectroscopic techniques. Single crystal X-ray data reveal that the complex assumes a trans-diaquo structure, [Cr(C17H18Cl2N2O4)]ClO4.H2O. The effect of phenyl ring substituents on the rate of formation of [O=Cr-V Schiff base](+) has been investigated. The bimolecular rate constant for the formation of O=Cr-V species by the [Cr(Schiff base)(H2O)(2)]ClO4, where the Schiff base=salprn, (1) and 5-chlorosalprn, (2) with PhOI was compared. In the case of (2) the rate was found to be faster by an order of magnitude at pH=4 compared to (1). The introduction of a chloro-substituent on the phenyl ring not only influences the rate of redox reactivity but also the pKa values of aquo ligands of the complexes, indicating the difference in the electronic environment around the metal ion in both (1) and (2).

Effect of molecular association on solubility, diffusion, and permeability in polymeric membranes

The filling-type membrane is composed of grafted polymer and solvent-resistant substrate; the calculation of solubility, diffusivity and swelling-suppression effect by the substrate permits the prediction of solvent permeability. As noted in our previous article, the use of this approach, called membrane design, resulted in accurate prediction of the permeability of aromatic compounds. In this study, the influence of hydrogen bonding on solubility and diffusivity is investigated both theoretically and experimentally. The solubility of chloroform and dichloromethane in poly(acrylate)s increases, and their diffusivity decreases, compared with that estimated without considering the hydrogen-bonding effect. Solubilities predicted by the lattice-fluid hydrogen-bonding (LFHB) model show good agreement with the results of vapor sorption. Comparison of diffusion coefficients measured by vapor permeation with those predicted from free volume theory reveals that the decrease of solvent diffusion coefficient is approximately proportional to the fraction of associated molecules. Fluxes of chloroform and dichloromethane were measured by vapor permeation experiments through filling-type acrylate membranes, and predictions agree well with experiments. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 171–181, 2000

Effects of molecular association on mutual diffusion: A study of hydrogen bonding in dilute solutions

Diffusivities of pseudoplanar molecules at trace concentration in methanol have been measured at 298.2 K using Taylor’s dispersion method. The data of the polar and nonpolar aromatic solutes are compared, and the effects due to solute–solvent interactions on diffusion, together with the solvation numbers, are determined. In this study, the effects are combined with the recently developed solute hydrogen-bond scales to unravel hydrogen bonding between solute and solvent. It is found that the degrees of association of the solutes with methanol decrease in the sequence hydroquinone>aromatic acids>phenols>aromatic amines>aprotic aromatic compounds. Except for o-nitrophenol, which is capable of intramolecular hydrogen bonding, all aromatic acids, phenols, and amines studied behave more as hydrogen-bond donor than acceptor in methanol. The present work also indicates that motions of associated molecules can be understood in terms of the molecular behavior of nonassociated solutes and the hydrogen-bond acidity/basicity of polar solutes.

The effects of molecular association on mutual diffusion in acetone

Limiting mutual diffusion coefficients of aromatic compounds in acetone have been measured at 298.2 K by using the chromatographic peak-broadening method. The data of the polar and nonpolar pseudoplanar solutes are compared, and the effects of molecular association on diffusion as well as the solvation numbers are determined. It is found that the effects of hydrogen bonding are such that –OH>–NH2>–SH, and that the solvation numbers are approximately equal for solutes containing the same polar group. Using ab initio molecular orbital theory, molecular solute–acetone interaction energies have been calculated. There exists a nearly linear relationship between the interaction energy and the effect of solute–solvent association on diffusion. The applicability of the rough-hard-sphere theory to the diffusion of associated molecules is discussed.

The effect of molecular association and tube dilation on the rotational viscosity and rotational diffusion in nematic liquid crystals

A combination of director reorientation experiments with dielectric relaxation spectroscopy was used to study the relation between the rotational viscosity γ1 and the rotational diffusion constants in nematic compounds with different association tendency. Increased values for γ1 were found for compounds showing strong association. This is explained by increased rotational friction of the associates due to the necessary translational motion of the molecules within these groups. For nonassociating compounds, γ1 was found to be described quantitatively by Marrucci’s theory, when, in addition, the tube dilation effect described by Doi for the rotational diffusion in an orientationally ordered environment is taken into account.

Effects of molecular association on structure and dynamics of a collagenous peptide.

Peptide GVKGDKGNPGWPGAPY from the triple-helix domain of type IV collagen aggregates in solution at a critical aggregation concentration of 18 mM. This molecular self-association process is investigated by 1H- and 13C-nmr spectroscopy. As a function of increasing peptide concentration, selective 1H resonances are cooperatively chemically shifted by up to 0.04 ppm to apparently saturable values at high concentration. Pulsed field gradient nmr was used to derive translation diffusion constants that, as the peptide concentration is increased, also cooperatively and monotonically decrease to an apparent limiting value. An average number of 6 monomer units per aggregate have been estimated from diffusion constant and 13C relaxation data. Comparative 1H nuclear Overhauser effect spectroscopy (NOESY) spectra accumulated at high and low peptide concentrations suggest that average internuclear distances are decreased as a result of peptide association. 13C-nmr multiple spin-lattice relaxation and 13C-[1H] NOE effects on 13C-enriched glycine methylene positions in the peptide demonstrate that overall molecular tumbling and backbone internal motions are attenuated in the aggregate state. Lowering the solution pD from pD 6 to pD 2 disrupts the aggregate state, suggesting a role for electrostatic interactions in the association process. Based on thermodynamic considerations, hydrophobic interactions also probably act to stabilize the aggregate state. These data are discussed in terms of an nmr/NOE constrained computer-modeled structure of the peptide.

Effect of molecular association on rheological properties of chitosan/acetic acid aqueous solutions (abstract)

Light scattering and rheological properties of chitosan solutions in 2% acetic acid aqueous solution were measured by means of a low angle laser light scattering photometer (Chromatix, KMX6) and a cone‐plate Weissenberg Rheogoniometer (Sangamo Controls, R18). Chitosan samples of CS62 and CS79, which have degrees of deacetylation of 0.62 and 0.79, respectively, associate even in very low concentrations such as 10−5 g/ml and a degree of association is 2–3. On the other hand, the molecular association does not occur in a chitosan CS96, which has a relatively high degree of deacetylation of 0.96. Rheological properties show that the solutions of CS62 and CS96 are homogeneous and the solutions of CS79 are heterogeneous, with a certain relaxation mechanism having relatively long relaxation times. The effect of the molecular association and the heterogeneous structure on stress overshoot is also discussed.