Molecular dynamics of germylacetylene

A complete vibrational analysis has been carried out for germylacetylene and germylacetylene-d₃ molecules and a set of molecular constants, i.e. kinetic constants and potential constants, is reported. The physical understanding of the nature of the potential constants and kinetic constants in molecules leads to a stringent application of provisions of group theoretical technique, introduced by Wilson in the study of molecular vibrations. This procedure is applied here to the evaluation of mean amplitudes of vibration. Coriolis coupling constants and centrifugal distortion constants of these cases, with highly satisfactory results. The values of Coriolis coupling constants and centrifugal distortion constants are in good agreement with the observed values for the germylacetylene molecule showing the significance of the procedure adopted in the present study.     

配合物的稳定性与配位体的酸碱强度之间的直线自由能关系VIII:N,N'-双(对位取代苯基)乙二胺与铜(II),镍(II)生成配合物的稳定性研究

在25℃, I=0.1mol.dm^-^3NaClO4的条件下,在混合溶剂[50%(υ/υ)二氧六环和70%(υ/υ)乙醇]中用pH法测定了N,N'-双(对位取代苯基)乙二胺的质子化常数及其与铜(II),镍(II)生成二元配合物的生成常数.结果表明:在配位体的质子化常数与配合物的生成常数之间,在配位体的σ'值与Hammett方程中的取代基常数σ之间,以及稳定化因子S~f与σ值之间,均存在着良好的线性关系.从实验进一步验证了在配位化学中直线自由能关系存在的普遍性.     

Ab initio study of spectroscopic constants and anharmonic force field of 74GeCl2

The equilibrium structure, spectroscopy constants, and anharmonic force field of germanium dichloride have been calculated at MP2, B3LYP, and CCSD(T) levels of theory employing two basis sets, cc-pVDZ and cc-pVTZ, respectively. The computed geometries, rotational constants, and vibration-rotation interaction constants, and quartic centrifugal distortion constants are compared with the available experimental data. The harmonic frequencies, anharmonic constants, and cubic and quartic force constants are predicted. The calculated results show that the MP2 results are in excellent agreement with experiment and represent a substantial improvement over the results obtained from B3LYP. The CCSD(T) method is also an advisable choice to study anharmonic force field of molecules.     

Calculation of gauche coupling constants from substituent electronegativities

The calculation of gauche coupling constants from substituent electronegativities by a method which takes into account the orientation of the substituents is described. This correlation has been derived from the coupling constants of disubstituted ethanes and has been applied to the calculation of coupling constants in cyclohexanes and 6-membered heterocycles. The detection of angular distortion in 6-membered rings from the difference between calculated and observed coupling constants is also described.     

Molecular dynamics of some X2Y3 systems

A complete vibrational analysis has been carried out for ¹⁰B₂O₃, ¹¹B₂O₃, and sulfur dicyanide and a set of molecular constants, i.e. kinetic constants, potential constants, compliance constants, vibrational mean amplitudes, Coriolis coupling constants and centrifugal distortion constants, is reported. The values of the centrifugal distortion constants of S(CN)₂, are in good agreement with the observed values, which bears out the significance of the method of kinetic constants adopted in this work.     

Chiral force constants: Recommendations for the presentation of internal coordinate force constants

Some force constants associated with the internal coordinates that sense handedness or chirality can have opposite signs in the enantiomers of chiral molecules. Examples of such force constants include interaction force constants between a torsional and stretching or bending internal coordinates. The sign reversal for these force constants in the enantiomers of chiral molecules or in opposite-handed molecular segments is best recognized by labeling them as chiral force constants. Recognition of chiral force constants suggests that certain guidelines are to be followed in the presentation of internal coordinate force constants. © 1993 by John Wiley & Sons, Inc. © John Wiley & Sons, Inc.     

Effects of nonequilibrium on velocity and plate height in reactive capillary electrophoresis

Models for velocity and plate height for reactive CE are developed under the formalism of generalized nonequilibrium theory, as described by Giddings. The resultant equations are consistent with chromatographic theory and validated with an independent stochastic simulation. Moreover, unlike prior methods for CE, this model allows calculation of thermodynamic equilibrium constants and kinetic rate constants from a single, undistorted peak. The theoretical development shows that velocity is directly dependent on the equilibrium constant and is independent of the rate constant. On the other hand, plate height varies little with equilibrium constant and is inversely proportional to rate constant. The ability to evaluate equilibrium constants from velocity and rate constants from plate height is most greatly influenced by electric field strength and mobility difference. The accuracy in calculated equilibrium constants is limited by mobility difference; however, the accuracy in rate constants is limited by plate height and equilibrium constant.     

Structural effects on the rates of the ion molecule reactions of organic heterocycles

Rate constants for proton transfer reactions of seven heterocyclic amines, eight heterocyclic ethers and propylene sulfide have been measured by photoionization mass specrometry. Rate constants for dimerization of four sulfides have also been measured. The measured rate constants have also been compared to the theoretical (ADO) rate constants. In all cases the ADO rate constants show only small variations with structure. In fact for the mono-heterocycles all but one of the ADO rate constants are between 2.0 and 1.5 × 10^?9 cc molec^?1 sec^?1. The observed rate constants show considerable dependence on chemical structure. The amines react faster than the oxides which in turn react faster than the sulfides. N-Methyl substitution on pyrrolidine and piperidine lowers their rate constants by about a factor of two while, propylene oxide reacts eighteen percent faster than ethylene oxide. Examination of the variation in the observed rate constants as a function of ring size for each group of heterocycles indicates a distinct structure-reactivity correlation although we have not attempted to rationalize this correlation. There is also a structure-reactivity dependence observed in the six-membered oxygen heterocycles having a second heteroatom O, NH, or S in the 4-position. The rate constants increase with the electronegativity of the second heteroatom.     

Application of the temperature dependence of vicinal spin-spin coupling constants to the investigation of the configuration of substituents in saturated 5-membered rings

Temperature dependence of cis- and trans-vicinal spin-spin coupling constants of substituted cyclic 5-membered compounds is discussed. The temperature dependence of trans-vicinal coupling constants is shown to be essentially stronger than that of cis-vicinal coupling constants if the energies of the conformers corresponding to potential energy curve minima are different. The temperature dependence of 33 vicinal spin-spin coupling constants has been studied for di- and trisubstituted thiophanes with a known configuration of substituents. Experimentally determined changes of trans-vicinal coupling constants with temperature are markedly larger than those for cis-vicinal coupling constants, whose values, in most cases, are practically temperature independent. Differences in the temperature dependence of cis and trans-vicinal spin-spin coupling constants can be applied for the determination of the configuration of substituents in saturated 5-membered rings.     

Analysis of Block and Statistical Copolymers by Gel Permeation Chromatography: Estimation of Mark-Houwink Constants

Abstract

A method is introduced for the estimation of Mark-Houwink constants of block and statistical copolymers. The homopolymer Mark-Houwink constants and copolymer composition are required. Use of estimated Mark-Houwink constants in GPC analyses gives results which agree well with those calculated with experimentally determined constants. Comparisons between this method and those of Runyon and coworkers (11) and Chang (12) are made for block copolymers. Chang's method was also extended to statistical copolymers, and where it compared closely with the one introduced here. The use of copolymer Mark-Houwink constants as a qualitative measure of polymer compatibilities in different solvents is also discussed.     

Hartree-Fock calculation of the harmonic force constants and equilibrium geometry of formaldehyde

Using the force method, complete sets of harmonic force constants have been obtained for formaldehyde from Hartree-Fock wavefunctions. The agreement with experiment is considered particularly satisfying for the off-diagonal constants. This holds not only for a near-Hartree-Fock Gaussian basis set but also for a small but polarized 7, 3/3/1 basis set. The value even of such a small calculation is underlined by frequencies calculated from force constants corrected for almost systematic errors in the diagonal constants. Experimental force fields are critically examined, and an explanation for the surprisingly large coupling between CO and CH stretching is indicated.     

Calculation of stability constants for the chiral selector-enantiomer interactions from electrophoretic mobilities

Interactions of chiral selectors with enantiomers or with other chiral analytes, underlying their electrophoretic separations, are particular cases of interactions of dissolved species. The interaction model that describes these reversible, fast interactions is simple. Equations describing the model are also simple and applying equations for the calculation of respective equilibrium constants to experimental data is easy using computers. Obtaining the experimental mobility data, necessary for the calculation, is the critical step on the way to stability constants quantitating the strengths of interactions of chiral selectors with enantiomers and other analytes. These data are decisive for both the accuracy and precision of the calculated constants. The meaning and applicability of the particular constant depend on the type of the constant. The common method for the determination of stability constants from electrophoretic migration data is reasonable for low and medium stability constants. For stronger complexing, characterised by stability constants of the order of 10(4) l/mol, typical of affinity chiral selectors, the method becomes unreliable. For strong complexing giving constants of the order of 10(5) or higher of or higher the method is not applicable in its commonly used form.     

在胆汁酸盐背景中n种氨羧配位剂的加质子常数及其钙配合物稳定常数

为测定在胆酸盐和脱氧胆酸盐存在下氨提配位剂的加质子常数和钙配合物稳定常数,对常规电住法做了一些修正。用所建立的方法测定了EDTA、DTPA、EGTA及NTA的有关常数及其随胆汁酸浓度的变化。     

Determination of dissociation constants for some pyrogallol azo derivatives and stability constants of their complexes with rare-earth metals

The dissociation constants of some haloazo derivatives of pyrogallol and the stability constants of their complexes with rare-earth metals (La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) are determined by potentiometric titration in aqueous ethanol (3: 7). A correlation between the dissociation constants of the reagents and the stability constants of their complexes is found.     

Miniglass,an interactive program for the evaluation of stability constants of metal/ligand complexes from potentiometric data

MINIGLASS is a microcomputer program for the treatment of pH titrations for evaluation of stability constants and adjustment of the parameters defining the titration curve. The program is written in PASCAL for the HP-200 computer series, and contains procedures for blank titrations, acidity constants and metal/ligand stability constants. Graphics support is provided for easy interaction with the user. The data files can be written by the editor of the operating system or can be created automatically from an automatic titration system. The program is tested for the determination of the formation constants of the well-studied Ni²⁺/glycine system. The results obtained agree well with literature values.     

Temperature dependence of physical constants in binary-fluorinated liquid crystal mixtures

The temperature dependence of dielectric constants and splay elastic constants for fluorinated phenyl bicyclohexane (PBC) binary liquid crystal (LC) mixtures is reported. The results show that the proportions of the constituent elements of binary mixtures strongly influence their anisotropic dielectric constants. For mixtures in which meta-para- and ortho-para-fluorine-substituted molecules are in equal proportion, the effectiveness of the anisotropic dielectric is equal to that with a single para-fluorine- substituted compound. The proportions of a mixture seldom affect the threshold voltage and splay elastic constants in an anti-parallel measurement cell.     

MBOHO calculations of phosphorus-carbon nuclear spin-spin coupling constants

Summary The novel generalized correlation of the nuclear spin-spin coupling constants with the atomic hybrids and net charges is employed to give a new relationship for calculating the directly bonded phosphorus-carbon coupling constants by use of the maximum bond order hybrid orbital procedure together with the extended Hückel molecular orbital calculation. The calculated coupling constants of phosphorus-carbon are all in good agreement with the experimental data, which shows that the new relationship obtained in the present paper is quite satisfactory for calculation of the phosphorus-carbon coupling constants.The project was supported by the National Natural Science Foundation of China and the Excellent University Teacher's Foundation of State Education Commission of China     

Fluorine NMR spectra of pentafluorophenyl derivatives

The fluorine chemical shifts and spin-spin coupling constants of 65 pentafluorophenyl derivatives with widely varying organic substituents were examined. Useful correlations of the three meta coupling constants with the chemical shifts of the para fluorine were found. It is suggested that these relationships be extended to all compounds of the type considered in order to determine the signs and approximate values of meta coupling constants. Equations for correlation of the fluorine chemical shifts with the Taft constants are presented. The possibility of calculating the Taft constants from the ¹⁹F NMR spectra of pentafluorophenyl compounds is being discussed.     

Relation between the structure and extracting power of higher tertiary amines

The effect of the composition and structure of higher tertiary amines on their efficiency in extracting nitric acid has been examined. The ionization constants of the amines in methanol have been determined by potentiometric titration. The extraction constants for nitric acid have been determined at constant ionic strength in the aqueous phase (μ=1). The dependence of these constants upon the concentrations and the degree of association of the amine salts in the organic phase has been examined. For the cases in which the role of steric factors is negligible it has been shown that at low amine salt concentrations in the organic phase there are quantitative regularities between the ionization constants of the amines in methanol, their extraction constants for nitric acid and the inductive effects of the substituents on the nitrogen atom.