Measurements of control rod worth by modified inverse kinetic method

Results of control rod worth measurements on the Astra critical assembly at the Russian Research Centre Kurchatov Institute are presented. The measurements were carried out by the modified inverse kinetics method, which is based on the use of experimental information about the variation of neutron detector readings only after introducing a reactivity perturbation. Calculated corrections are not required. The results of measurements do not depend on the neutron detector position.     

Synthesis by radical polymerization and structure of drag reducing terpolymers based on acrylamide,acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid

Russian Journal of Applied Chemistry - Terpolymers of acrylamide, acrylonitrile, and sodium 2-acrylamido-2-methylpropanesulfonate were prepared by radical copolymerization in aqueous solution. The...     

Insights into the reaction paths of copper(i) acetylides with dichloroglyoxime leading to 3,3′-biisoxazoles

Russian Chemical Bulletin - Base-free reaction of dichloroglyoxime with copper(i) acetylides gave 3,3′-biisoxazoles via a nucleophilic substitution of the chlorine atom of dichloroglyoxime...     

Solvent-free telomerization of isoprene with alcohols catalyzed by palladium(ɪɪ) carbene complexes

Russian Chemical Bulletin - The effect of various factors on the activity and selectivity of palladium N-heterocyclic carbene (NHC) complexes in the telomerization of isoprene with alcohols has...     

In search for a pentacoordinated monoorgano stannyl cation

Alkylation of Sn(OCH₂CH₂NMe₂)₂ (1) by MeI or MeOTf leads to a mixture of quaternary ammonium salts by alkylation of the NMe₂ moiety. Reaction of Sn(acac)₂ (2) with MeOTf gives unexpected redistribution product Sn(acac)OTf (3), which is a rare example of mono acetylacetonato tin (II) derivatives. Pentacoordinated monoorgano stannyl cation was generated by salt metathesis from PhSn(OCH₂CH₂NMe₂)₂Cl (5) and Ag[Al(OCH(CF₃)₂)₄] or Ag[B(C₆F₅)₄]. This cation was not isolated due to its strong electrophilic nature. It abstracts substituents from aluminate and borate weakly coordinating anions (WCAs) leading to redistribution products [Al[OCH(CF₃)₂]₂OCH₂CH₂NMe₂]₂ (6) and [Ph(C₆F₅)Sn(OCH₂CH₂NMe₂)₂][H₂OB(C₆F₅)₃] (9), respectively. Structures of 3 and 6 were established by single-crystal X-ray diffraction analysis.     

Effect of hydrogen bonding on the structure and vibrational spectra of the complementary pairs of nucleic acid bases. II. adenine-thymine

The vibrational spectra of an isolated complementary adenine-thymine pair are calculated in the B3LYP/6-311++G(d,p) approximation and analyzed. The effect of hydrogen bonds on the structure is shown along with the position of frequencies and intensities of normal vibrations of the pair in comparison with the spectra of isolated thymine and adenine molecules. A comparative analysis of the hydrogen bonding effect on the IR and Raman spectra of thymine and adenine is performed     

Thermal neutrons from the earth’s surface during the upper and lower transits of the moon and the sun on new moon and full moon days

The times of increases in the thermal neutron flux from the earth are compared with the passages of the moon and the sun at the longitudes of the observation sites on July 26, 1991, July 27, 1991, July 12, 1995, July 29, 1996, and July 21, 1997 (the upper and lower transits of the moon and the sun). The results confirm the role of tidal forces in the generation of thermal neutron fluxes from the earth’s surface. The study uses the astronomical annuals of the Russian Academy of Sciences for the corresponding years.     

Heteroorganic betaines. 8. Synthesis and structures of silicon- and germanium-containing organoarsenic betaines R13As+—CR2R3—EMe2—S– (E = Si,Ge)

The reactions of ylides R¹ ₃As=CHR² with hexamethyl-2,4,6-trisila- and hexamethyl-2,4,6-trigermatrithiacyclohexanes afforded betaines R¹ ₃As⁺—CHR²—SiMe₂—S^– (2) (R¹ = Et; R² = Ph (a), Me₃Si (b); R¹ = R² = Ph (c)) and Et₃As⁺—CH(SiMe₃)—GeMe₂—S^– (3), respectively. Betaines 2a,b and 3 were characterized by multinuclear NMR spectroscopy. According to the X-ray diffraction data, in the crystals the As⁺—C—E—S^– main chain (E = Si or Ge) of molecules 2a,b and 3 adopts a twisted cis conformation due to strong intramolecular Coulomb interactions between the anionic and cationic centers. The equilibrium geometries of isolated molecules 2a and 3, which were calculated within the framework of the density functional theory (the PBE functional, the TZ2P basis set), are in qualitative agreement with the X-ray data. In solutions, betaines 2a (in the absence of Li salts) and 2c (in the presence of LiBr) selectively decomposed according to the Corey—Chaykovsky reaction, which was accompanied by elimination of R₃As and, probably, the intermediate formation of silathiirane. The subsequent transformation of the latter afforded 2,2,4,4-tetramethyl-5-phenyl-2,4-disila-1,3-dithiolane.     

Features of synthesis of fatty acids in active lipid-forming yeasts

Features of the accumulation of fatty acids and the changes in their composition in seven strains of yeasts that are promising producing agents of lipids have been studied. It has been shown that in the process of accumulation of lipids in the biomass changes take place that lead to a fall in the degree of unsaturation of the pool of fatty acids. This nature of the change in the composition of the fatty acids is, as has been shown by measuring their absolute amounts in the biomass, connected with the intensive synthesis of oleic and palmitic acids as components of the reserve lipids. The results obtained form the basis for an evaluation of the promising nature of individual strains as active producers of fatty acids.Moscow Technological Institute of the Food Industry. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 788–791, November–December, 1988.     

Molecular geometry and electronic structures of stable organic derivatives of divalent germanium and tin [(\operatorname{Me} _3 \operatorname{Si} )_2 \operatorname{N} {\kern 1pt} ---{\kern 1pt} Me_2 ]_n (M = Ge, n = 1; M = Sn, n = 2): a theoretical study

The molecular geometry and electronic structure of stable organic derivatives of divalent germanium and tin, [(Me₃Si)₂N-M-OCH₂CH₂NMe₂]_n (M = Ge (4), n = 1; M = Sn (5), n =2) and their isomers with broken (4a, 5a) and closed (4b, 5b) intramolecular coordination bonds M←NMe₂, were studied by the density functional (PBE/TZ2P/SBK-JC) and NBO methods. Factors responsible for stability of their dimers 4c and 5c were established. Dimerization of 5b in the gas phase is a thermodynamically favorable process (ΔG ⁰ = ?2.1 kcal mol^?1) while that of 4b is thermally forbidden (ΔG ⁰ = 10.1 kcal mol^?1), which is consistent with experimental data. The M←NMe₂ coordination bond energies, ΔE ⁰, were found to be ?5.3 and ?8.6 kcal mol^?1 for M = Ge and Sn, respectively. NBO analysis showed that the metal atoms M in molecules 4 and 5 are weakly hybridized. The lone electron pairs of the M atoms have strong s-character while vacant orbitals of these atoms, LP* M, are represented exclusively by the metal np_z-AOs. The strongest orbital interactions between subunits in dimers 4c and 5c involve electron density donation from the lone electron pairs of oxygen atoms (LP O) to the LP* M orbitals.