Studies in nuclear magnetic resonance—XII: Complete analysis of the proton spectra of tert-butylcyohexane-3,3,4,4,5,5-d6 and -3,3,5,5-d4

Accurate parameters for the two title compounds have been obtained by the aid of a spectral subtraction technique in conjunction with analysis by LAOCN3. It is observed that J_{1eq, 6eq} and J_{1ax, 2ax} are abnormally large and small, respectively, and the significance of these and other coupling constants are discussed in terms of the probable geometry of tert-butylcyclohexane. The tert-butyl group affects the chemical shifts of the 4-protons, indicating that tert-butylcyclohexyl derivatives are poor models for fixed conformers of monosubstituted cyclohexanes. The deuterium isotope effects on proton chemical shifts appear to be influenced by the same factors as proton-proton coupling constants.     

First-order Kondo-frustated antiferromagnetic ordering in the heavy electron compound YbAs

¹⁷⁰Yb Mössbauer measurements show that the heavy electron compound YbAs undergoes a first order paramagnetic-antiferromagnetic transition centered at T_N=0.58K. The saturated 4f-shell magnetic moments are reduced by 47% relative to the value predicted by a crystal field model. A study of the line shapes below T_N in the presence of an external field shows that the RKKY exchange energy is about 20 times bigger than k_B T_N. These results show that YbAs presents a magnetic order frustrated by the Kondo effect.supported by CNPq     

Zur Kenntnis des Härtungsprozesses von Phenol-Formaldehyd-Harzen

Zusammenfassung Durch Hydrierung, Abbau und durch Vergleich des Verhaltens linearer Mehrkernverbindungen bei diesen Reaktionen wurde neuerdings experimentell geprüft, ob die annahme, daß gewisse Härtungsprodukte von Phenolalkoholen cyclische Struktur besitzen, zutrifft.     

The determination of the magnetic structure of DyCrO4 by neutron diffraction

At room temperature DyCrO₄ has the tetragonal zircon structure. Susceptibility measurements show that DyCrO₄ is ferromagnetic below 23 K. Neutron diffraction from a powder sample yield the magnetic structure. Using a computer program, which was developed for the determination of non-collinear and spiral structures, several models allowed by symmetry were compared with the experiment. It turns out that the Dy-moments and the Cr-moments as well order parallel in the a-b-plane. For the Dy-moment a value of 12μ_B and for the ratio of the Cr- to the Dy-moment a value of $\text{1}\text{10}$ was found.     

Magnetic properties of the cerium monochalcogenides

Single crystals of CeS, CeSe and CeTe have been investigated by means of measurements of the specific heat, the thermal expansion, the magnetic susceptibility and the magnetization at low temperatures. Crystal-field effects on some of these properties are used to derive the crystal-field splitting of the 4f electron ground state. It is found that chemical composition and crystal perfection strongly influence the magnetic properties of these compounds.     

Synthesis of deuterated methyl 2,3,4,6-Tetra-o-methyl-β-d-galactopyranosides

Conclusions We have synthesized methyl 2,3,4,6-tetra-O-methyl--D-galactopyranosides selectively labeled with deuterium in positions 1–6 with deuterium content >90%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 192–195, January, 1978.     

Synthesis of polysaccharides. Communication 15. Synthesis of β-(1 → 6)-D-galactan

Conclusions 1,2-0-(1-exo-Cyano)ethylidene-3,4-di-0-acety1-6-0-trityl- and 1,2-0-(1-exo-cyano)ethylidene-3,4-di-0-benzoyl-6-0-trityl--D-galactopyranoses were synthesized. Their polycondensation led to D-galactans, which do not contain -glycoside bonds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya., No. 10, pp. 2358–2363, October, 1984.