The preferred conformations of 2,4-dichlorophenol, 2,4-dichloroanisole and their sulphur analogues

Analysis of the benzene dipole moments of 2-chloroanisole and 2,4-dichloroanisole, 2-chlorothioanisole and 2,4-dichlorothioanisole shows these compounds to exist as trans. 2-Chlorophenol and 2,4-dichlorophenol, and their sulphur analogues, are mixtures of Cis and trans conformers. The populations of the cis conformers are, at 25°C, 86 and 78% for the phenols, and ca. 70 and 50% for the corresponding thiophenols. The influence of various factors, such as the non-additivity of the (2-ClC₆H₄X)-group moment and torsional oscillation of the H-X bond (especially the H-S bond), on the calculated populations has been discussed. Incidentally it has been shown that p-dimethoxybenzene and p-di-(methylthio)benzene, as well as p-phenylenediamine and p-diformylbenzene, are equimolecular mixtures of cis and trans conformers.     

Estimation of the ground state correlation energy for isoelectronic series of 2 to 20 electrons

Correlation energies for all isoelectronic sequences of 2 to 20 electrons andZ=2 to 25 are obtained by taking differences between theoretical total energies of Dirac-Fock calculations and experimental total energies. These are pure relativistic correlation energies because relativistic and QED effects are already taken care of. The theoretical as well as the experimental values are analysed critically in order to get values as accurate as possible. The correlation energies obtained show an essentially consistent behaviour fromZ=2 to 17. ForZ>17 inconsistencies occur indicating errors in the experimental values which become very large forZ>25.     

Photothermal degradation of copolymers of methyl methacrylate and n-butyl acrylate

The photothermal degradation of copolymers of methyl methacrylate (MMA) and n-butyl acrylate (n-BuA) covering the whole composition range has been studied at 165°.The gaseous products, which are relatively minor, are hydrogen, carbon monoxide and methane. The liquid products are predominantly MMA, with n-BuA, n-butanol and n-butyraldehyde as minor products. Infra-red spectral changes in the residue were attributed to lactone formation and associated with butanol formation as in the purely thermal reaction The “cold ring” or chain fragment fraction becomes increasingly more abundant as the n-BuA content of the copolymer is increased.All the products and principal features of the reaction are explained in terms of a radical process which is initiated by scission of pendant acrylate units and is propagated by a combination of depropagation and intra- and intermolecular transfer processes, the relative importance of which depends upon copolymer composition. Differences from the thermal reaction and the corresponding reaction in copolymers of methyl methacrylate and methyl acrylate are discussed.     

Activity coefficients of the binary mixtures of o-cresol or p-cresol with C1–C4 aliphatic alcohols near ambient pressure

Bubble point temperatures near ambient pressure, for the binary mixtures, formed by o-cresol or p-cresol with – methanol, ethanol, n- and iso-propanols and n-, iso-, sec- and tert-butanols – covering the whole composition range, are measured using a Swietoslawski-type ebulliometer. The liquid phase composition–bubble point temperature measurements are found to be well represented by the Wilson model. Values of the optimum Wilson parameters as well as the computed values of vapor phase mole fractions and activity coefficients are tabulated. The results are discussed in terms of isomerization with reference to the selected set of compounds, constituting the mixtures and the stearic effects in the cresols.     

Syntheses of methylpyridine and methylpyridine N-oxide decorated benzoxazine and naphthoxazine platforms

Simple, aqueous-based syntheses of methylpyridine and methylpyridine N-oxide decorated 3,4-dihydro-2H-naphthoxazine and 2,3-dihydro-1H-naphthoxazine monomers, as well as thermally promoted syntheses of 3,4-dihydro-2H-benzoxazine monomers and bisoxazine methylpyridine derivatives of substituted 1,5-, 2,6-, and 2,7-dihydroxynaphthalenes are described. The crystal structures of two derivatives are presented.     

Asymmetric nitrone cycloadditions and their application to the synthesis of enantiopure pyrrolidine and pyrrolizidine derivatives

The cycloaddition reactions of a pair of chiral pyrroline-N-oxides derived from d-ribose with some typical mono and disubstituted alkenes are reported. In all these reactions with monosubstituted alkenes as well as with dimethyl maleate the preferred stereochemical outcome of the cycloaddition step comes from a 5-exo-anti transition state whereas stereoisomers from the 5-exo-syn transition state are also present as minor adducts. In the reaction with dimethyl fumarate the major adduct comes from a 4-exo-5-endo-syn transition state. The further behavior of the obtained isoxazolidines upon reductive ring opening conditions depends on the kind and the geometry of the preexisting substituents and they are transformed to enantiomerically pure pyrrolidine or pyrrolizidinone derivatives.     

ΔF = ±2 transitions in the hyperfine spectrum of Er I

The occurrence of 15ΔF=±2 transitions in the hyperfine spectrum of five lines of Er I was observed by means of high-resolution laser-atomic-beam spectroscopy. These normally forbidden transitions are caused by an external magnetic field which mixes closely lying hyperfine levels that have neighbouringF quantum numbers. If the Zeeman splittings under the applied magnetic field are small compared to the hyperfine splittings, the intensities of theΔF=±2 components are proportional to the square of the magnetic field strength. Under the variation of the laser intensity theΔF=±2 transitions show the same behaviour as homogeneously broadenedΔF=0, ±1 transitions. The relative intensities between theΔF=±2 components as well as the intensity ratios of theΔF=±2 to neighbouringΔF=±1 components are studied and interpreted in terms of first order perturbation theory.     

Phase transition and thermodynamic properties of TiN under pressure via first-principles calculations

The phase transition of TiN from the NaCl structure to the CsCl structure is investigated by the first-principles plane wave pseudopotential density functional theory method, and the thermodynamic properties of the NaCl structures are obtained through the quasi-harmonic Debye model. It is found that the pressures for transition from the NaCl structure to the CsCl structure are 364.1 GPa (for GGA) and 322.2 (for LDA) from equal enthalpies. The calculated ground state properties such as equilibrium lattice constant, bulk modulus, and its pressure derivative are in good agreement with experimental and theoretical data of others. Moreover, the dependences of the relative volume V/V ₀ on the pressure P, the Debye temperature ?? _D , and heat capacity C _V on the pressure P and temperature T, as well as the variation of the thermal expansion ?? with temperature and pressure are also successfully obtained.     

Interrelation between side chain crystallization and dynamic glass transitions in higher poly(n-alkyl methacrylates)

Calorimetric and dielectric results for crystallizable poly(n-alkyl methacrylates) (PnAMA) with C=12, 16 and 18 alkyl carbons per side chain are presented. Degree of crystallization D_cal and melting peak temperature T_M are estimated from conventional DSC measurements. For poly(n-hexadecyl methacrylate) (C=16) the influence of isothermal crystallization is studied by DSC as well as TMDSC. Changes in dielectric relaxation strength Δε and α peak shape during crystallization are investigated. Effects of side chain crystallization on the complex dynamics of PnAMA are discussed. The results are related to the relaxation behavior of lower nanophase-separated PnAMA with two co-existing glass transitions, the conventional glass transition (a or α) and the polyethylene-like glass transition (α_PE) within alkyl nanodomains formed by aggregated alkyl rests. It is shown that amorphous as well as semicrystalline PnAMA can be understood as nanophase-separated polymers with alkyl nanodomains having a typical dimension of 1-2 nm. The results are compared with the predictions of simple morphological pictures for side chain polymers. X-ray scattering data for the amorphous and semicrystalline PnAMA are included in the discussion. Common aspects of nanophase-separated systems in both states as well as differences caused by crystallization are discussed. Indications for the existence of rigid amorphous regions are compiled. Different approaches to explain a similar increase of T_g(α_PE)—the glass temperature of the amorphous alkyl nanodomains—and T_M—the melting temperature of crystalline alkyl nanodomains—with side chain length are considered. Pros and cons of both approaches, based on increasing order within the alkyl nanodomains and confinement effects in nanophase-separated systems, are discussed. Main trends concerning crystallization and cooperative dynamics are compared with those in other systems with self-assembled nanometer confinements like microphase-separated blockcopolymers or semicrystalline main chain polymers.     

Chemical identification and determination of sulfonamides in n-component solid mixtures within THz-region--solid-state Raman spectroscopic and mass spectrometric study

The identification and quantitative determination of sulfonamidesin solid-state as n-component mixtures is performed. The limits of detection (LODs), accuracy, precision and repeatability are obtained and discussed, using the Raman spectra within 200-30 cm⁻¹ region (6.00-0.9 THz). The excitations, corresponding to H-bonding deformations, lattice vibrations, as well as coupling modes are used for determination. The validation of the statistical and mathematical tools for procedure of the spectroscopic patterns is performed. The possibilities of baseline correction methods, smoothing procedures, and non-linear curve fitting method for quantitative analysis within THz-region for complex spectroscopic patterns of n-component mixtures (n = 1-5) are discussed. The hybrid HPLC tandem mass spectrometry (MS/MS) and powder XRD are applied as independent physical methods for analysis of the studied systems.     

Electrochemical behavior of nitroxy radical monolayers prepared on tin oxide electrodes by the Langmuir—Blodgett method: An unusual effect of concentration of supporting electrolytes on cyclic voltammograms

The photoemission current (j) and the differential capacitance of the double layer (C) on 20-200 nm thick bismuth films have been measured. The current j as a function of potential (E) follows the 5/2 law for films of thickness exceeding 80 nm and for bulk bismuth. The current j as a function of E for thin films exhibits steps whose width increases as the thickness decreases. The absolute values of j and C also decrease for thinner films. These effects are manifestations of the quantum size effect in the energy spectrum of charge carriers in bismuth. Estimations of the degree of metallization of the bismuth surface are presented.     

Dielectric and raman spectroscopic studies on the rotational isomerism of t-butyl formate

Static dielectric constants, refractive indices and densities have been measured for t-butyl formate and acetate in cyclohexane at increasing concentrations and at two temperatures, 20°C and 60°C. The ΔH value for the cis-trans equilibrium of t-butyl formate and the dipole moment of the trans conformation has been calculated from the dielectric measurements taking the ΔS value calculated from the sum-over-states for the cis and trans conformations and assuming the dipole moment of the cis conformation to be equal to 1.94 D as found for t-butyl acetate, which has the cis conformation only.The relative intensities of the Raman bands corresponding to specific vibrations modes of the cis and trans conformations of t-butyl formate are measured in cyclohexane and acetonitrile at various concentrations. The enthalpy difference ΔH is also measured in the liquid state and in acetonitrile by variation of the intensity ratio of the bands with temperature.All thermodynamic quantities obtained from dielectric or Raman intensity measurements are compared with each other and with the theoretical values. The solvation energy difference between cis and trans conformations in cyclohexane and acetonitrile as well as in the liquid state are also compared with theoretical values. The large deviation of solvation energy difference between the experimental value and Onsager's model value are well described by an additional term, which considers dipole-dipole interaction.     

An expedient synthesis of 2,5-disubstituted-3-oxygenated tetrahydrofurans

Single enantiomer 2,5-disubstituted-3-oxygenated tetrahydrofurans are synthesized in as little as four steps from a commercially available epoxide. The key steps are homoallylic alcohol epoxidation, palladium-catalysed alkoxy-carbonylation-lactonisation and Mitsunobu inversion. The protocol is applied to the formal total syntheses of (+)-kumausallene, (6S,7S,9R,10R)-6,9-epoxynonadec-18-ene-7,10-diol and the core of lytophilippine A.     

Polyvinylpyrrolidone thin film pyrolysis as accessed by the real-time optical transmission measurements

Present results reveal basic features of the optical transmission thermo-analytical method in its employment to investigate the oxidative pyrolysis of supported thin polyvinylpyrrolidone films. The OT curves naturally vary in shapes and positions on the time/temperature scales, respective to the examined rate of sample heating, to the wavelengths of radiation as well as to the film thickness. Recorded OT curves exhibit characteristic shapes with well-expressed OT minima. The temperatures at which the OT minima appear are in a linear relationship with heating rates of samples, at a frequency of radiation as well as a film thickness kept constant. Similarly, the OT values at which the OT minima appear are in a linear relationship with film thickness, at a frequency of the radiation and sample heating rate unchanged.     

Ant venom alkaloids from Solenopsis and Monorium species: Recent developments

The chemistry and biology of the ant venom alkaloids from the genera Solenopsis and Monomorium are briefly reviewed. The usual 2,6-dialkylpiperidines found in four as yet unstudied species of Solenopsis are described. In addition, a monoalkylated 1-piperideine, that is a new natural product, is described from a fifth Solenopsis species. Finally, the venoms of Monomorium latinode and M. subopacum are shown to contain an array of 2,5-dialkylpyrrolidines.     

Photochemical chlorination of alkanoic acids anchored to a polymeric support

The synthesis of 2-(poly-p-styryl)ethyl esters of hexanoic, heptanoic, octanoic, nonanoic and decanoic acids as well as (poly-p-styryl)methyl octanoate and poly-2-(nitro-p-styryl)ethyl octanoate are described and their photochlorination are studied and compared with the monomeric (conventional) photochlorination of the methyl, benzyl and 2-phenylethyl esters of these acids. Hypotheses are advanced to explain the results on monochlorination products.     

Determination of phosphorus:glycerol:acyl ratios in phospholipids

Phospholipids (1–5 mg) are mixed with methyl heptadecanoate as an internal standard. One part of the sample is reduced with Vitride in tetrahydrofuran in a sealed tube at 50 2C for 1 hr. The reaction products are acetylated in the same tube by treatment with acetic acid-acetic anhydride at 140 °C. After 1 hr total O-acyl and after 16 additional hours glycerol are determined as the fully acetylated compounds by gas-liquid chromatography.Another part of the sample is subjected to acidic hydrolysis and total O-acyl and N-acyl groups are determined by GLC as fatty-acid methyl esters. The aqueous phase is heated to 100 °C with 6 N HCl for 72 hr and phosphorus is measured colorimetrically.     

DFT studies of copper complexes with biphenyldiimino dithioether. Part III: AIM analysis

The electronic structure of tetrabenz[a,e,g,k]-15,18-dithia-9,24-diaza-cyclohexadeca-9,23-diene (bite), as well as its quasi-tetrahedral and quasi-planar Cu(bite)^q complexes (q = +1 or +2), has been investigated at the MP2/6-31G level of theory in terms of atoms-in-molecule (AIM) topological analysis of electron density. The electron density ρ, its Laplacian L and bond ellipticity ε at bond critical points (BCP) as well as atomic volumes and atomic charges evaluated using the electron density integrated over atomic basins are correlated with the formal Cu oxidation state, coordination polyhedron geometry and mechanical strain data. The greatest changes in AIM parameters are concentrated at the central CuS₂N₂ part of the systems under study. The deformations of the electronic structure of the active center due to mechanical strain may be crucial for electron transfer. Atomic charges and bond strengths are compared with the results of natural bond orbital treatment.     

Synthesis and analytical applications of sodium N-bromo-p-nitrobenzenesulfonamide

Sodium N-bromo-p-nitrobenzenesulfonamide (bromamine-N) is useful as an oxidizing titrant. The synthesis, composition and structure are reported. Direct titrations of ascorbic acid, glutathione, thioglycolic acid, methionine, sulfite and arsenite are described. The procedures are simple and rapid; errors are within ± 0.5%. The compound is a somewhat better titrant for those species than the chlorine analogs such as chloramine-T and chloramine-N.     

The elastic strain energy of crystallographic shear planes in reduced tungsten trioxide

The elastic strain energy in reduced tungsten trioxide, which contains crystallographic shear (CS) planes, has been calculated using Fourier transform theory. This allows the effects of non nearest-neighborCS planes to be evaluated, and also enables one to assess the relaxation energy of ions in theCS planes as well as the strain energy of the matrix between theCS planes. The results are presented for{10m} (2 ? m ? 7) and {001}CS plane types. They are compared with experimental data and also with the results of previous calculations using classical elasticity theory.