Precise values of the 13C component vicinal coupling constants for calculating side-chain conformations in amino acids

From consideration of ¹H–¹H vicinal coupling constants and ¹³C? ¹H long-range coupling constants in a series of amino acid derivatives, the precise values of ¹³C component vicinal coupling constants have been calculated for the three minimum energy staggered rotamers for the C(α)H? C(β)H₂ side-chains of amino acids.     

A high yield synthesis of (±)-5,8-dimethoxy-2-α-hydroxyethyl-3,4-dihydronaphthalene,a key intermediate in anthracyclinone synthesis

The dimethoxytetralol ($\text{2}$) gives on Vilsmeier reaction the dihydronaphthaldehyde ($\text{3}$) (yield,92%), which on Grignard reaction with MeMgI affords the title compound ($\text{6}$) (yield,~100%), the reactions constituting a high yield synthesis of this important anthracyclinone intermediate.     

Absorption spectra of Cu2+ in shattuckite and plancheite

Optical and EPR measurements are carried out on shattuckite, a copper bearing silicate. The EPR spectrum observed at 120 K reveales hyperfine structure for parallel and perpendicular components. The measured values are g6 = 2.402, g⊥ = 2.038, A6 = 112 × 10^-4 cm^-1 and A⊥ = 49.5 × 10^-4 cm^-1 and they indicate a tetragonal distortion for the Cu²⁺ion. Further, the constants P and K are evaluated and found to be 0.014 cm^-1 and 0.0112 respectively. The bands observed at 8160, 13330 and 16125 cm^-1 are assigned to the electronic states of Cu²⁺, in a crystal field subjected to tetragonal (C_4V) distortion. The crystal field parameters evaluated are Dq = -1333, Ds = -1565 and Dt = -380 cm^-1. Correlating the EPR and optical data, the orbital reduction factors are calculated as k6 = 0.89 and k⊥ = 0.59. It is confirmed from EPR and optical studies that the Cu²⁺ion in shattuckite is sited in an elongated octahedron. Similar studies are carried out for plancheite. The observed optical absorption spectrum of plancheite is attributed to Cu²⁺ sited in an elongated octahedron and tetragonal field parameters are evaluated.     

Studies in the formation of heterocyclic rings containing nitrogen

Synthesis of 1-benzyl-3-methyl (I), 1-beazyl-3-substituted benzyl (II) and 1-methyl-3-substituted benzyl (III)-2-aryl benzimidazolines is described. (I) acc obtained by the condensation of N¹benzyl-N²methyl-o-phenylenediamine with various aldehydes in metharol. Compounds (II) are prepared from N¹-benzyl-N²-arylidene-o-phenylenediamines in acetic acid, through a process of disproportionation involving an oxidation-reduction process. Likewise, (III) are obtained from N¹-methyl-N²-arylidenc-o-phenylenediamines. The exact structure of N¹-benzyl-N²-arylidene-o-phenylenediamines which can exist in the open chain form or in the ring form has been investigated using nmr spectroscopy.     

Entropy and enthalpy of formation and migration of lattice defects in Na(I)

The self-diffusion coefficients of Na⁺ and I^?, as well as the ionic conductivity, are measured in Na(I) single crystals, pure and doped with Ca²⁺ ions. The computer analysis of the whole set of data shows that the atom transport in Na(I) is ensured essentially by the free vacancies with a very small contribution (～4%) of the vacancy pairs. The thermodynamic parameters of vacancy formation and migration are derived by taking the long range interactions into account (activity coefficients on the concentrations and relaxation factors on the mobilities). The respective entropies of Schottky defect formation, cation migration and anion migration are equal to 7.64, 3.23 and 2.91 k while the corresponding enthalpies are equal to 2.00, 0.58 and 0.77 eV.     

The dynamic analysis of circular plates and shallow spherical shells

In the investigation reported here an attempt has been made to study the influence of Berger's approximation on the non-linear transient response of circular plates and shallow spherical shells. The governing equations of motion obtained from Berger's approximation are solved by using the rapidly converging Chebyshev series spacewise and the Houbolt scheme for integration in the time domain. Results calculated when using Berger's approximation are compared with exact results. It is shown that Berger's method yields very accurate values for plates and shells under transient loading, in the case of immovable edge conditions.     

Potentiometric estimation of thorium as oxalate

Summary The potentiometric determination of thorium as oxalate yields values with a constant error and therefore can be employed for analysis with a suitable correction.

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Zusammenfassung Die potentiometrische Thoriumbestimmung als Oxalat liefert Werte mit konstantem Fehler und kann daher mit entsprechender Korrektur zur Analyse verwendet werden.

     

A method for the simultaneous estimation of228Th and229Th

A simple method is reported in this paper to estimate²²⁹Th in the presence of²²⁸Th. The total activity of²²⁹Th and²²⁸Th was determined by following the alpha activity growth (using a liquid scintillation counter and proportional counter) of purified thorium samples. The activity ratio of²²⁹Th/²²⁸Th was determined by alpha spectrometry. From the initial total activity and ratio, disintegration rates of²²⁹Th and²²⁸Th were calculated. The values obtained for the activities have a precision better than ±2%.     

A short regiospecific total synthesis of furoventalene,a marine natural benzofuran

Synthesis of a naturally occurring irregular isoprenoid benzofuran, furoventalene ( 3 ), has been achieved in high yield via the nickel catalyzed coupling of 4-methyl-3-penten-1-ylmagnesium bromide ( 1 ) with 3-methyl-6-chlorobenzofuran ( 2 ).