Magnetochemistry of dimers with iron group ions

General theory of matrix interactions of dimers of iron group ions is considered. Equations for calculation of matrix elements of the exchange energy of dimers and equations for calculation of the magnetic moments of dimers of different d ⁿ configurations and different exchange parameters are reported. The energies of the spin states of dimers are calculated with inclusion of exchange interactions of the first J ₀ and second J ₂ orders, and energy state diagrams for dimers with different spins and exchange energies are reported. For heterospin dimers, equations for calculation of the magnetic moment ?? and magnetic susceptibility ?? are introduced, and for homospin dimers, analytical formulas of calculation are presented. The tables of magnetic moments are calculated and their diagrams as a function of J ₀ for homospin dimers with spins S = 5/2, 2, 3/2, 1, and 1/2 are given. The experimental data are interpreted for Co²⁺ dimers as an example: the experimental and theoretical dependences of ?? and ?? on temperature are considered.     

Qualitative and quantitative measurements of radioiodines

Some methods for measurements of radioiodines are discussed. Three isotopes of iodine are presented in detail;¹²⁵I,¹²⁹I and¹³¹I. Limited discussions of¹²³I and¹²⁶I are also given. Measurements of these isotopes are examined for both the NaI(TI) and liquid scintillation systems. The properties of the decay schemes are utilized to explain the mode of measurements of the isotopes in these two types of detectors. Methods of standardization of the radioiodines are discussed. Special emphasis is given to the direct standardization of¹²⁵I as compared to so called “Mock¹²⁵I” standards.     

A high resolution mass spectrometric measurement system for a vacuum fusion apparatus

A high resolution mass spectrometric read-out system for a vacuum fusion apparatus is described. Rapid analyses are possible and the rate at which various gases are evolved can be monitored. Gas mixture assays are accomplished by scanning the nominal mass 28 peak. Serial measurements of CO⁺, N₂⁺ and C₂H₄⁺ are made. Thus detection and measurement of evolved hydrocarbons are possible. The results for silver and tin from a conventional vacuum fusion apparatus and the mass spectrometer apparatus are compared.     

A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

Intramolecular NH…O,S,N interactions in non-tautomeric systems are reviewed in a broad range of compounds covering a variety of NH donors and hydrogen bond acceptors. ¹H chemical shifts of NH donors are good tools to study intramolecular hydrogen bonding. However in some cases they have to be corrected for ring current effects. Deuterium isotope effects on ¹³C and ¹⁵N chemical shifts and primary isotope effects are usually used to judge the strength of hydrogen bonds. Primary isotope effects are investigated in a new range of magnitudes. Isotope ratios of NH stretching frequencies, νNH/ND, are revisited. Hydrogen bond energies are reviewed and two-bond deuterium isotope effects on ¹³C chemical shifts are investigated as a possible means of estimating hydrogen bond energies.     

Bulk Free‐Radical Co‐ and Terpolymerization of n‐Butyl Acrylate/2‐Ethylhexyl Acrylate/Methyl Methacrylate

n‐Butyl acrylate (BA), 2‐ethylhexyl acrylate (EHA), and methyl methacrylate (MMA) are commonly used monomers in pressure‐sensitive adhesive formulations. The bulk free‐radical copolymerizations of BA/EHA, MMA/EHA, and BA/MMA are studied at 60 °C to demonstrate the use of copolymer reactivity ratios for the prediction of BA/MMA/EHA terpolymer composition. The reactivity ratios for BA/EHA and MMA/EHA copolymer systems are determined using low conversion experiments; BA/MMA reactivity ratios are already known from the literature. The reactivity ratio estimates for the BA/EHA system are r _BA = 0.994 and r _EHA = 1.621 and the estimates for MMA/EHA are r _MMA = 1.496 and r _EHA = 0.315. High conversion experiments are conducted to validate the reactivity ratios. The copolymer reactivity ratios are shown to predict terpolymer composition of high conversion BA/MMA/EHA experiments.     

Early Stages of Crystallization in Gel Derived ZrO2 Precursors

Three different precursor materials giving rise to contrasted nanostructures, xerogels, aerogels and precipitates, are prepared by a sol gel route in the Zrn -propoxide—acetylacetone—water—n-propanol system. Clear homogeneous gels are made by using a proper amount of acetylacetone and water. The gels are dried either by conventional processing (xerogels) or by supercritical evacuation of alcoholic solvent (aerogels). The complexation ratio (R = [acetylacetone]/[Zr(OR)₄]) is the main parameter controlling the size of ZrO₂ primary particles. WhenR = 0 , precipitates are obtained.Xerogels, aerogels and precipitates are characterized and their textures are compared through small angle X-ray scattering measurements. The fractal structure of gels is destroyed by conventional drying and is preserved in aerogels. On the other hand precipitates are described as homogeneous agglomerates of very small primary units.The first crystallization steps are studied by transmission electron microscopy and X-ray diffraction experiments. The contribution of crystallite size and microstrain effects are investigated by Rietveld whole pattern fitting. The crystallization of precipitate powders starts at the agglomerate scale with large crystal like distorted lattices.     

Structure formation under negative pressures

IR and Raman spectroscopy are used to study cubic and orthorhombic modifications of Sb₂O₃. Vibrational spectra are calculated in the approximation of density functional theory; the bands are assigned. Based on the assignment made, vibrational spectra of the α-Sb₃O₂F₅ compound are analyzed.     

Spectra-structure relationships in the near ultraviolet optical activity of chiral barbituric acid derivatives

The chiroptical properties associated with then-π^* (singlet-singlet) transitions in dissymmetric barbituric acid derivatives are examined on the basis of two theoretical models. The lower singlet excited states of unsubstituted and alkyl substituted barbituric acids are calculated on the semi-empirical CNDO/S-CI molecular orbital model, and the spectroscopic properties associated with transitions to these states are computed. In the structures we examined, threen-π^* transitions are found at λ>220 nm, two of which are nearly degenerate. Each of these transitions is computed to be strongly magnetic dipole allowed and to be forbidden or very weak (depending upon the exact symmetry and geometry of the trioxopyrimidine moiety) in electric dipole radiation. Contributions from chiral distortions within the trioxopyrimidine chromophoric system to the rotatory strengths of the three lowest energyn-π^* transitions are calculated directly from wave functions obtained by the CNDO/S-CI method. Contributions to then-π^* rotatory strengths arising from “vicinal” interactions between the trioxopyrimidine chromophore and asymmetric substituent groups are calculated by a perturbation method based on an independent systems representation of the optically active compounds. Various spectra-structure relationships are considered and correlations between experimental data and theoretically calculated results are examined.     

The routine determination of boron,carbon, nitrogen and oxygen by charged-particle activation analysis

Normalized parameters for the determination of boron, carbon, nitrogen and oxygen are given. The irradiations are performed with 9 MeV protons or 7.5 MeV deutons. The beam current is measured with a Faraday cup and beam current fluctuations are corrected for by a computer calculation. The samples are automatically counted on a time schedule based upon the half-lives. Counting data are evaluated by means of computerized least squares decay analysis. Absolute sensitivity factors with the dimension dpm⁻¹ μA⁻¹(g/cm²)⁻¹ are determined.     

Über die Matrixisolation von AsCl4F

Matrix Isolation of AsCl₄F The gasphase components during the sublimation of [AsCl₄]⁺[AsF₆]^? are characterized by means of mass and IR matrixisolation spectroscopy. The primary vaporization products are AsF₅ and the new halide AsCl₄F. The IR spectra of AsCl₄F and PCl₄F are compared and the calculated force constants are discussed. Other mixed halides of arsenic are formed under suitable conditions.     

Antibiotics Produced by Bacillus Bacteria

Data for antibiotics produced byBacillusbacteria and structural formulas of the antibiotics gramicidin, tyrocidine, bacitracin, mycobacillin, surfactin, bacilysin, and subtilin are presented. Various biosynthetic mechanisms and chemical properties are discussed. The lantibiotics, which are produced by certainBacillusspecies and have unique structural features different from those of other antibiotics, are analyzed. Structural formulas of unusual amino acid residues in lantibiotics are presented and their mechanisms of biological action are examined     

Theoretical rate constant calculations for O(3P) with saturated hydrocarbons

Theoretical rate constants have been calculated for O(³P) with five saturated hydrocarbons, CH₄, C₂H₆, C₃H₈, iso-C₄H₁₀, and neo-C₅H₁₂. The method of choice is bond energy–bond order (BEBO) with activated complex theory (ACT). Because the BEBO method is empirical, O(³P) + CH₄ is evaluated first, and the theoretical results are compared to more rigorous calculations and to the empirical transition state method. Comparisons are also made between predictions and experimental results. All of these comparisons show that the BEBO-ACT method gives results which are consistent with experiment and other theory. Because the method is successful, the other four cases are then considered. Ambiguity arises for the higher hydrocarbons from the problem of internal rotations in the activated complexes, and three cases are evaluated. Best agreement with experiment is obtained if the primary rotor(s) in the complexes are considered to be free. Predictions of rate constants are made from 500 to 2500 K. Throughout the discussion issues of theory which are common to any ACT calculation from any method of potential energy evaluation (LEP, LEPS, or ab initio quantum mechanics) are featured.     

Amine catalysis in phosphoryl transfer from 2,4-dinitrophenyl phosphate in aprotic and protic solvents

Reactions of tetra-n-butylammonium 2,4-dinitrophenyl hydrogen phosphate, (ArPH)^?(R₄N)⁺, in aprotic and protic solvents, in the absence and in the presence of alcohols or water, ROH, are compared with analogous reactions of the salt in the presence of hindered and unhindered amines, e.g. diisopropylethyl amine and quinuclidine. Similar studies are performed with the acid, ArPH₂, in the presence of variable amounts of amines. The release of phenol and the fate of the phosphorus compounds are followed by ¹H and ³¹P NMR spectrometry. In the absence of free unhindered amine, reactions of the monoanion are relatively slow, sensitive to steric hindrance in the alcohol, and incapable of producing t-butyl phosphate from t-butanol; reactions of the dianion are relatively fast, insensitive to steric hindrance in the alcohol, and produce t-butyl phosphate. In the presence of free unhindered amine, reactions of the monoanion are relatively fast but still sensitive to steric hindrance in the alcohol, and hence do not produce t-butyl phosphate. The intermediate CH(CH₂CH₂)₃⁺NP(O)(OH)O^? is detected in the presence of quinuclidine. Reactions of the dianion in the presence of unhindered amines are analogous to those observed in the presence of hindered amines. The uncatalyzed and the nucleophilic amine-catalyzed reactions of the monoanion are assumed to proceed via oxyphosphorane, P(5), intermediates. The dianion reactions, which are not susceptible to nucleophilic catalysis, are assumed to proceed via the monomeric metaphosphate ion intermediate, PO₃^?. Significant effects related to solvent properties are observed in these reactions.     

A density functional computational investigation on electronic properties of the stable irregular boron fullerenes with 20–56 atoms

The various irregular B_n (n=20‐56) cages are optimized at the B3LYP/6‐311G level. The geometries and electronic properties are systemically discussed. New B₂₄ and B₂₈ geometries are revealed. The calculated results show that the number of polygonal vacancies is apparently increased as the size of irregular cages being increased and that the irregular cage configurations with uneven distribution of different sized holes enhances the stabilities of the fullerenelike cages. The magic numbers of stabilities are predicted to be B₄₈. HOMO and LUMO gaps are discussed. Furthermore, the delocalized π orbitals are mainly distributed around the polygonal vacancies of irregular cages and enhance the stabilities of the irregular boron cages. © 2015 Wiley Periodicals, Inc.     

Carbon-13 NMR spectroscopy of hop bitter substances

The ¹³C NMR spectra of the most important hop bitter substances are analysed. All individual carbon atoms are assigned, except the oxygen bonded sp² carbon atoms. Most assignments are made partly by comparison with analogous compounds and partly by reference to literature data. Cross-correlations with the ¹H NMR shifts are made for two main products and confirm the correctness of the assignments. All data are in agreement with the known structures.     

Molecular spectra and optical investigation of dissociation and ionization of simple gases by electron collisions

This paper reports investigations of the VUV emission spectra which are produced by electron impact of simple molecules. Some new features in the emission spectrum of the N₂ molecule are given. Furthermore, new measurements of the dissociative excitation of N₂ and H₂O are reported and the excitation mechanisms are discussed.     

A full vibrational assignment (4000-50 cm−1) of 1, 10-phenanthroline and its perdeuterated analogue

Full infrared and Raman vibrational assignments (4000-50 cm⁻¹) of 1,10-phenanthroline are presented and full infrared assignments (4000-50 cm⁻¹) of 1,10-phenanthroline-d₈ are given. Four fundamentals are newly reported for 1,10-phenanthroline and several changes are recommended to earlier assignments for this compound. The assignments of the fully deuterated analogue are newly reported.     

Crossed-beám chemiluminescence. II. Kinetics and mechanisms for reactions of group IIA Metals in ground and metastable states with fluorine

Visible chemiluminescence technique under crossed-beam conditions has been applied to the study of the reactions of the group IIA metal atoms Mg, Ca, Sr and Ba in their ground state (¹S₀) or in an excited metastable state (³P_i, ³D_i or ¹D₂) with F₂. The monofluoride emission bands are the most prominent features in the chemiluminescence spectrum. Using higher fluorine densities radiation is observed from excited alkaline earth difluorides, which are shown to principally originate from secondary reactions. Formations of MF* are determined to be first order with respect to both the metal atom and the fluorine molecule. Total cross sections for removal of ground state metal atoms from the beam by F₂ are 115 ± 15Ų for Ca, 125 ± 15Ų for Sr, and 160 ± 15Ų for Ba, which is consistent with an electron jump model. Chemiluminescence cross sections are reported for the reactions involving electronically excited reactants M*. Photon yields of 12 ± 3% for Mg*, 18 ± 5% for Ca*, 20 ± 5% for Sr*, and 15 ± 8% for Ba* reacting with F₂ are measured. These high photon yields are remarkable when compared with absolute photon yields for the ground state reactions which indicate that less than 2% of the products are MF* molecules. It was possible to obtain vibrational state distributions for some of the excited monofluorides which are found to be populated in a non-thermal manner. This strongly suggests that the dynamics of the reactions are governed by a direct mechanism. From the crossed-beam chemiluminescence spectra the dissociation energies of the ground state monofluorides are estimated. In addition, improved spectroscopic constants, dissociation energies and dissociation products of some of the excited electronic states of MF are given.     

Long range 13C?13C coupling constants. A review

A large number of ¹³C? ¹³C coupling constants from a diversity of compounds are now available. Attempts have been made to classify this information in order to illustrate how these data are obtained, how signs are determined and how both two- and three-bond couplings can lead to structural information. Coupling constants in aromatic compounds are now well documented, substituent effect trends have been established and correlations with bond orders are noticed. Comparison of ¹³C? ¹³C couplings with ¹³C? ¹H couplings is mentioned. Theoretical calculations are dealt with, and these can now be properly evaluated as both magnitudes and signs of the experimental couplings are known. Finally, the occurrence of long range couplings in biosynthetic material is briefly surveyed.