Advances in Molecular Relaxation and Interaction Processes最新文献

A complete molecular dynamic study of monoacetylferrocene has been carried out in p-xylene using dielectric relaxation measurements in the frequency range of 700 MHz-38 GHz at temperatures of 293, 303, 313, and 323 K and at concentrations that vary from 0 to 3% by weight. Under these conditions no intermolecular association or interaction of any type was observed between the solute molecules. As was expected, the compound absorbed in the GHz-region, there being just one very sharp band. At the present stage of our inquiry, this may be assigned to rotation around the molecular axis perpendicular to the two cyclopentadienyl rings or to the molecular reorientation. Treatment of the real and imaginary parts of the complex dielectric permittivity obtained at a concentrarion of 3% (weight fraction) clearly confirmed that the behaviour is very similar to that predicted by the Debye theory. The following macroscopic dielectric relaxation times were calculated: T/K, τ/ps; 293, 26.15; 303, 22.88; 313, 20.66; 323, 18.31. Analysis of these data by means of an Eyring diagram gave the following values for the parameters of the activation of the dielectric relaxation process: ΔH*=1.63±0.3 kcal.mol⁻¹ and ΔS*=−4.86 e.u.

In transient relaxation method studies of fast reactions, if the rate of response of the chemical system is comparable with that of the perturbation, the exact shape of the forcing function must be taken into account in the kinetic treatment of the relaxation response. An analysis of the transient response of multiple coupled equilibria using Laplace transform is presented for various forms of step or impulse perturbation. The method enables one to calculate the relaxation amplitudes for an unrestricted number of coupled chemical equilibria. Various aspects of the analysis of the relaxation response are discussed.

The ¹H NMR spectra have been obtained for a number of H-bonded complexes formed by the interaction of OH-acids of increasing strength and [(CH₃)₂N]₃PO (HMPT) in a freon mixture (CDF₂Cl + CDFCl₂) at 100 K.The signals of the complexes with moderately strong acids (pK_a> −2) are singlets,which proves that they have a molecular structure,AH…B.With stronger acids,a doublet spin-spin coupling of the bridge proton with ³¹P nucleus occurs (J_PH=cca 20 Cps) indicating a complete proton transfer,A⁻…HB⁺.The conclusion has been drawn that a sharp change in structure is caused by gradual change in the interaction energy as measured by ΔpK_a.The spectra of a number of conjugated complexes,[BHB]A⁻,have been taken.If B=B,the homoconjugated cation with a centrosymmetric H-bond is formed,followed by a strong decrease in J_PH.

Dielectric relaxation measurements were carried out on mono-, and 1,1′-di-benzoylferrocene in p-xylene in the temperature and frequency range of 293–313 K and 7.5–38.2 GHz, respectively, at various concentrations. For both molecules only one absorption was found in the GHz-region, which can be assigned to whole molecule reorientation and/or (less probably) to the internal rotation around the axis perpendicular to the cyclopentadienyl rings. In both cases a Debye-like behaviour was observed. The following macroscopic dielectric relaxation times (τ) were calculated: compound, T/K, τ/ps; monobenzoylferrocene, 293, 39.8; 303, 37.3; 313, 35.0; dibenzoylferrocene, 293, 63.2; 303, 51.9; 313, 41.2. From the Eyring diagram values of 1.6 and 2.3 kcal.mol⁻¹ were obtained, respectively, for the activation enthalpy of mono-, and di-substituted derivative. A comparison was made among the various ferrocenes studied to date in our laboratory.

An EDA complex, formed by 4,4′diacyldiphenyl (I) and N,N′dialkyl-4,4′diaminodiphenyl (II), which possesses liquid crystalline phases, has been investigated by ir spectroscopy. The EDA interaction is indicated by the yellow colour of the complex. The electronic stack interaction is remarkably enhanced by hydrogen bonds, which act in the plane of the aromatic rings. This has been demonstrated by comparison with a system formed by (I) and the N,N′dimethylated compound II. Although the latter compound is strongly related to II, it lacks proton donor ability. Further D/H isotope exchange has been used to investigate the problem.

A double zeta quality SCF-MO calculation is reported for the C₆H₆…HF complex. The hydrogen bond distance and strength are reported together with various one-electron properties. Changes in electron distribution on complex formation are discussed. The likely accuracy of the results is inferred from the agreement between previous theoretical and experimental results on the HCN…HF complex.

The importance of unpaired spin distribution in the Co(II)-Dopamine complex in aqueous solution, was investigated. From the analysis of the H-1 and C-13 isotropic shifts and with the aid of an INDO M.O. calculation on a dopamine radical a prevalent σ-type delocalization mechanism of the spin density was evidentiated, even if a contribution from π-electrons cannot be completely excluded.

The analysis of the spin-lattice relaxation rates revealed the importance of ligand-centered dipolar interactions. The introduction of the spin densities, calculated from the INDO method, in the modified Solomon-Bloembergen equation, allowed to estimate the correlation time of the complex which can be identified with the electronic relaxation time.

Empirical formulae for evaluating the dielectric relaxation intensity, or the magnitude of dielectric dispersion, from dielectric loss data, proposed by Kita and Koizumi, in a limited range of frequency around the relaxation frequency for the Davidson - Cole relaxation has been verified in the case of three i-alkyl halides.

The relaxation intensity Δε is expressed in terms of ε′_M′ the dielectric loss maximum and W the frequency separation for a half, two thirds or three quarters of ε′_M′ in the form