Advances in Molecular Relaxation Processes最新文献

The effect of changing the ∠ CO … H on the energy of the linear hydrogen bond has been studied by ab initio calculations for one formamide-methane complex and two formamide-water complexes, which differ in the position of the second hydrogen (H2₀) of the water molecule (i.e. the one not involved in the hydrogen bond). When the hydrogen bond is cis to the CN bond (∠ CO … H  120°), this hydrogen is, respectively, trans (1) and cis (II) to the CO bond. It is found that the formamide-methane complex has two minima with hydrogen bond energies of ∼; −2.6 kcal mol⁻¹, at values of about 120° and 240° for the ∠ CO … H. The barrier height at 180° is ∼; 0.9 kcal mol⁻¹. A different situation is found for the formamide-water complexes, where the hydrogen bond energy is largely dependent on the position of H2₀. The formamide-water (I) complex has one minimum of −10.74 kcal mol⁻¹ for the hydrogen bond at a value of ∼; 110° for ∠ CO … H. The energy rises sharply with changes in the angle, and is −7.54 kcal mol⁻¹ at 180°. The other complex (II) has one minimum of −9.14 kcal mol⁻¹ at 240° and a hydrogen bond energy of − 7.12 kcal mol⁻¹ at 180°. It is also found that the hydrogen bond length increases in a regular manner when ∠ CO … H changes from 120° to 240°.

Measurements of spin lattice ¹³C-relaxation times of protonated carbon atoms in monosubstituted diphenyls are described. It was possible to obtain the various T₁-times as a function of the anisotropic Brownian rotation by application of Woessner's theory. Two diffusion rates for the “overall” motion were derived from the T₁-values. It was ascertained that the anisotropy of rotation is fundamentally greater than the theoretical value, owing to the mass moments of inertia. This is caused by the very high “frictional effect” on the C_xy-rotation. The intramolecular rotation of the phenyl group was determined by two models of motion. The barrier of rotation was obtained from quadrupole T₁-data. These barriers are nearly the same as the values obtained using quantum-mechanics. The dependence of the barrier of rotation upon Hammett's σ_m-parameter is evident.

CNDO/2 calculations for hydrogen bond interaction of H₂0 and HF and the charge transfer interaction of chlorine with benzene have been carried out. While the dissociation energies for hydrogen bond interactions are satisfactory, they are large for charge transfer interactions. The axial model for the chlorinebenzene interaction has been found to be more stable.

The infrared spectrum of solid KHC1₂C₄O₄ has the characteristic features of intermolecularly bonded acid salts of carboxylic acids. The X-ray structure analysis of the crystals belonging to the space group P1̄, revealed two crystallographically different, strong hydrogen bonds of the same O … O distance 2.449(2) $\text{\$}\text{̊}$linking the dichloromaleate units into one-dimensional arrays parallel to the (1 1 1̄) direction. The infrared spectra of the solution of KHC1₂C₄O₄ and of (C₄H₉)₄NHCl₂C₄O₄ indicate intramolecular hydrogen bonding.

In (I), we describe a numerical method for determining the relaxation distribution function from decay curves. The distribution function is expanded in a series of appropriate polynomials and the best values of the coefficients are determined by the method of least squares. In order to examine its applicability and limit, we apply it to some artificial decay curves constructed with different types of distribution functions. According to the results, our method is more adequate for the continuous distribution than for the discrete one. Accurate calculation is very effective so long as the original decay data are accurate, while rough calculation is good when the original decay data are rough or include some noise. Therefore, rough calculation is practical for analysis of experimental decay data which are not free from errors.

In (II), we apply our method to the decay process of electric birefringence of several concentrated poly-γ-benzyl-L-glutamate solutions. It is sometimes necessary to modify the experimental data because of improper selection of the base line. The semi-logarithmic plot is effective for modification. In order to make our physical image clearer, the length distribution function is introduced. Field strength dependence, time dependence and concentration dependence of the length distribution curve have been obtained. Our method is powerful for investigating a systematic change of the distribution function with changes of external or internal conditions.

The infrared spectrum of charge transfer complexes formed between pyridine derivatives (H, CH₃, C₂H₅, Cl, Br, I) and IC

Formal analysis of dielectric data on dilute solutions of rigid polar molecules in non-polar solvents yields a second (high frequency) absorption regio

The dependence of third-order nonlinear electric polarization on low and high electric field vibration frequencies in isotropic molecular media is disc