H bonding of substituted pyridines on silica

The infrared spectra of a series of substituted pyridines which were adsorbed on silica have been obtained. A linear correlation is obtained between the wavenumber shift of the OH stretching fundamental of the surface hydroxyl groups towards lower wavenumber and the Hammett polar substituent parameter of the adsorbate. Deviations are only observed for tert.-butyl substituents in ortho-position and for ortho-substituents which render a dual interaction with neighbouring OH groups possible. The optical density of an IR continuous absorption is a function of the proton affinity of the adsorbate and it can be explained by assuming the formation of protonated adsorbed species which exhibit symmetrical NH⁺… N bond.     

Electron-transmission study of the temporary anion states of substituted pyridines

Electron-transmission spectroscopy has been employed in a study of the temporary negative-ion states of 2-, 3- and 4-methylpyridine, 2-, 3- and 4-chloropyridine, 2-, 3- and 4-aminopyridine, 2-, 3- and 4-acetylpyridine and 2- and 4-vinylpyridine. The effect of substitution on the normally unoccupied orbitals, as well as that of replacement of a CH group by a nitrogen atom, is found to be related to the coefficient of the molecular orbital at the site of substitution. The latter effect, however, is much less pronounced for the unfilled than for the filled orbitals. We attribute this to changes in geometry of the aza derivatives and to the greater diffuseness of the anion wavefunction compared with that of the cation.A simple Hückel MO treatment, the equivalent of the LCBO method for filled orbitals, is applied to the unfilled orbitals of the vinylpyridines and acetylpyridines, and yields the energies of these short-lived anion states quite satisfactorily.     

14N nuclear magnetic resonance of some monosubstituted pyridines

The ¹⁴N chemical shifts of some monosubstituted pyridines are reported. They show a correlation with the electronic nature of the substituent which is not found with earlier ¹⁴N chemical shift data. The shifts may be satisfactorily explained in terms of the average excitation energy approximation if both π- and σ-bond polarization is considered by means of SCF-MO calculations and ¹⁴N nuclear quadrupole resonance data. The ¹⁴N N.M.R. line widths are discussed from the point of view of molecular reorientation processes in the liquid state.     

He(I) and He(II) photoelectron spectra of some substituted ethylenes

The He(I) and He(II) photoelectron spectra of acrolein, acrylic acid, methyl acrylate, vinyl acetate, acrylamide and some of their methyl-substituted analogues are reported. Detailed assignments are proposed, mainly based on differences in intensity between the He(I) and He(II) spectra, on sum rule considerations and on the results of modified CNDO/S calculations.The assignment criteria are critically evaluated.     

Mixed ionic and electronic conductivity study of charge transfer complexes of some substituted pyridines with iodine monochloride (ICl) by AC impedance spectroscopy

Mixed ionic and electronic conductivity of three solid charge transfer (CT) complexes of pyridine, 4-methylpyridine (γ-picoline) and 3,5-dimethylpyridine (3,5-lutidine) with ICl (iodine monochloride) are reported. Electrical parameters of the prepared complexes in the pellet form are evaluated at various temperatures and at wide frequency range by employing AC complex impedance spectroscopic technique. Suitable equivalent circuits for the Nyquist plots, which provide the most realistic model of the electrical properties of the CT complexes, have been suggested. Both transport number measurements and impedance spectra reveal that the conduction in γ-picoline-ICl complex is mainly due to ions, in 3,5-dimethylpyridine-ICl complex, it is due to both ions and electrons and in pyridine-ICl complex, it is predominantly due to electrons. The a.c. conductivity measurements of the CT complexes have been carried out in the frequency range of 10–10⁵ Hz within the temperature range of 303–353 K. The variation of a.c. conductivity with frequency follows the Jonscher’s universal power law. The temperature dependence of electrical conductivity suggests the semiconducting behaviour of the materials.     

Calculation of some characteristics of substituted benzenes

Compounds of the C₆H₅XY₁Y₂ type have been examined, and the dependence of energy and wave functions ona _Y, ß_XY and ß_CX has been studied. Numerical calculations have been carried out and tables compiled.In conclusion the authors would like to thank N. A. Prilezhaev and V. I. Danilov, who helped us daily in carrying out this work.     

Photoelectron spectra of some fluorine substituted diazanaphthalenes

The high resolution He 584 Å photoelectron spectra of fluorine substituted 1,2-diaza-, 1,3-diaza-, 1,4-diaza- and 2,3-diaza-naphthalene are presented. By means of fluorine substitution the analysis of the photoelectron spectra of the parent compounds can be made more definite. Unexpected shifts of the nitrogen “lone-pair” bands can be explained within the through-space and through-bond interaction model. From this explanation one can deduce that fluorine substitution can give experimental evidence about the symmetry character of the “lone-pair” molecular orbitals.     

The laser gain characteristics of some substituted coumarins

A theoretical and experimental study has been made of the small signal gains of six coumarin dyes (DAMC, 4 MU, 7 HC, calcein blue, esculin and scopoletin) in a common solvent (ethanol), and the variation correlated with the different substituents in the coumarins. The relative variation in gain, taking the value for DAMC as the basis, is about 75% for 4 MU, 7 HC and calcein blue, 55% for esculin and 20% for scopoletin. The total tunable range for these dyes is from 430–530 nm. The higher gain in the case of DAMC is attributed to the relatively higher intramolecular charge transfer in this dye compared to the hydroxy-coumarins. The different substituents in the hydroxy-coumarins studied appear to have only a marginal influence on the gain.     

High resolution hydrogen resonance spectra of some substituted ethylenes

The olefinic proton resonance spectra of a number of mono- and 1, 2 di-substituted ethylenes have been analysed as AB, ABC or ABX systems to obtain the coupling constants and chemical shifts. The values of J _trans (range observed 13·7 to 18·0 c/s in 14 compounds) were significantly larger than J _cis in similar molecules. The values of J _cis (range observed 6·5 to 12·3 c/s in 8 compounds) are abnormally large when the olefinic bond is conjugated to an aromatic ring. Coupling between adjacent protons in an olefinic methylene group (J _gem) is much smaller, and sometimes negative. The shielding of the lone vinyl proton in mono-substituted ethylenes is smaller than that of the methylene group and in two cases (the vinyl group directly bonded to an oxygen atom) the difference is so great as to give an approximation to the ABX condition, so that the methylene protons appear to be shielded to an unusually large extent.     

Nambu-Poisson dynamics with some applications

Short introduction in NPD with several applications to (in)finit dimensional problems of mechanics, hydrodynamics, M-theory and quanputing is given.     

Studies of hyperfine splittings and spin distributions of the lowest excited triplet states of substituted benzenes and pyridines

Hyperfine splittings and linewidths of the E.P.R. spectra of the lowest excited triplet states of several cyano-substituted benzenes, pyridines and 1,2,4,5-tetrachlorobenzene were studied, and spin distributions were estimated. These spin distributions as well as the zero field parameters were discussed in terms of the modified benzene π electron MO. It is shown that one excited configuration dominates in the studied systems, but a small amount of configuration mixing is necessary in order to explain ZFS. The experimentally determined spin densities were compared with those calculated from UHF methods in the case of benzonitrile and phenylacetylene. The calculated spin densities agree well with those estimated experimentally when proper choice of integral is made. It is also shown that the spin distributions in triplet state and radical anions are similar in the systems studied here. The geometries of the excited triplet states of substituted benzenes are also investigated from UHF calculation.     

Lattice dynamics of some binary alloys

Summary The phonon dispersion frequencies for Cu₃Au, Cu₃Zn and Ni₃Fe alloys have been calculated using the model potential approach. The contribution of a short-range three-body interaction to the dynamical matrix has also been included in the present study. The theoretically computed phonon dispersion curves of these alloys are found to be in good agreement with the experimental data.     

Molecular dynamics and time reversibility

We present a time-symmetrical integer arithmetic algorithm for numerical (molecular dynamics) simulations of classical fluids. This algorithm is used to illustrate, through concrete examples, that time-asymmetric evolutions are typical for systems of many particles evolving according to reversible microscopic dynamics and to calculate the asymptotic behavior of the velocity autocorrelation function with an improved accuracy. The equivalence between equilibrium time averages and microcanonical ensemble averages is checked via two new sampling methods for computing microcanonical averages of classical systems.     

分子动力学模拟尺寸对纳米Cu颗粒等温晶化过程的影响

采用分子动力学方法和镶嵌原子势, 模拟了4000个Cu原子和13500个Cu原子(简称Cu₄₀₀₀和Cu₁₃₅₀₀)组成的纳米颗粒以及块体Cu的等温晶化过程. 通过对这些颗粒在晶化过程中结构和动力学行为的分析研究, 发现低温时, 不同尺寸的纳米Cu颗粒均出现多步晶化, 且晶化时间的分布曲线远比高温时范围大; 除了温度, 颗粒尺寸对晶化行为也有重要的影响, 尺寸越大, 晶化时间越长, 最终的晶化程度越高; 但是晶化时间随尺寸增大而增加的趋势不会一直持续, 发现存在一个临界尺寸r_c, 小于r_c时, 晶化时间随颗粒尺寸增大而增加, 大于r_c时,晶化时间随尺寸增大而减小.