Automated determination of fluoride ion in the parts per milliard range

Fluoride, down to 2 ppM, has been determined by automated direct potentiometry using a fluoride ion-selective electrode. The method reduces the dilution and contamination effects of TISAB and takes the electrode response-time into consideration. The relative standard deviation for water samples is 1.5-1.8% and the recovery varies from 96 to 107%.     

Conformations of fused cycloalkanes in organometallic complexes : IV. The crystal and molecular structure of tricyclo-[6.4.0.02.7]dodeca-3,5-dienetricarbonyliron

The precise molecular structure of the title compound has been determined by single crystal X-ray diffractometry. It consists of a cyclohexadiene ring fused at the 5 and 6 positions to a cyclobutane ring which is in turn fused to a cyclohexane ring. The two six-membered rings are trans to each other with respect to the shared four-membered ring. The Fe(CO)₃ moiety is bound in the usual way to the conjugated diene portion of the cyclohexadiene ring. The feature of greatest interest is the mutual influence of the conformations of the two fused cycloalkane rings, whose intrinsically preferred conformations are mutually incompatible. Under the influence of the fused cyclohexadiene ring the C₄ ring would tend to be planar, while the cyclohexane ring would tend, of itself, to have a chair conformation. The actual result is a compromise, with the C₄ ring being folded by 15° along its diagonal and the C₆ ring having a conformation intermediate between planarity and a chair. Crystallographic data: space group, P2₁, Z = 2. Unit cell dimensions at 3°C are a = 6.176(1), b = 11.307(2), c = 9.781(2) Å and β = 92.89(2)°. A set of 1733 reflections having 2θ(Mo-K_α) < 63.7° and I > σ(I) was refined to convergence (R₁ = 0.055; R₂ = 0.034) with hydrogen atoms refined isotropically and all others anisotropically.     

Simulation of intermolecular and intramolecular interactions of nucleic acid subunits by means of atom–atom potential functions

Atom–atom potential functions for calculation of nonbonded interaction energies of nucleic acids are proposed. Quantitative reliability of the obtained results is checked by using the calculations of intermolecular interaction energy in crystals. Based on the calculations of the interaction energy of the nucleic acid bases the molecular mechanisms of spontaneous mutations are suggested.     

Connection between the electronic structure of tin in its compounds and the isomer shifts in the Mössbauer spectra

A formula is obtained which relates the isomer shifts in the Mössbauer spectra to the electronic structure of tin in its compounds. It is shown that these formulas describe the isomer shifts of various kinds of chemical compounds: tetravalent tin with -bonding (tin tetrahalides), tetravalent tin with no -bonding (compounds in which the tin is bound to alkyl, aryl, or metal carbonyl radicals), divalent tin, etc. The formulas are used to analyze the electronic structures of tin in compounds of these classes. It is shown that in tetravalent tin compounds with -bonding the isomer shift in the negative direction (with respect to -Sn) is due to the decreased number of 5s-valence electrons, and in the absence of -bonding, by an increase in the number of 5s-valence electrons.     

Synthesis and Properties of First Bis(fluoreno)crownophanes

Alkylation of 2,7-dihydroxy-9H-fluoren-9-one with 2-(2-chloroethoxy)ethanol, 2-[2-(2-chloroethoxy)-ethoxy]ethanol, and 2-{2-[2-(2-chloroethoxy)ethoxy]ethoxy}ethanol in dimethylformamide in the presence of potassium carbonate gave 78–80% of the corresponding diols which were treated with p-toluenesulfonyl chloride in a dioxanechloroform mixture in the presence of triethylamine at 0– 5°C (30 h). The resulting bis(p-toluene-sulfonates) were brought into condensation with 2,7-dihydroxy-9H-fluoren-9-one in a very dilute solution in dimethylformamide containing anhydrous potassium carbonate at 80–85°C. Appropriate treatment of the reaction mixture, followed by chromatographic purification afforded 53–27% of the first representatives of a new class of cyclophanes, bis(oxofluoreno)crownophanes. Raising the temperature to 95–105°C resulted in an appreciable decrease of the product yield. The yield of the target products did not increase on replacement of potassium carbonate by cesium carbonate.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 1, 2005, pp. 144–149.Original Russian Text Copyright © 2005 by Lyapunov, Kirichenko, Kulygina, Luk’yanenko.     

Synthesis of Sybstituted Isoxazoles and Pyrazoles Based on 1-Aryl-3,4,4-trichloro-3-buten-1-ones

3-Aryl-5-methylenehydroxyiminoisoxazoles were synthesized by reaction of 1-aryl-3,4,4-trichloro-3-buten-1-ones with hydroxylamine. Reactions of ketones with hydrazine provided pyrazole structures; therewith two pyrazole molecules underwent coupling affording 3-arylpyrazole-5-carbaldehyde azines.     

The Effect of Surface Forces on the Thermal Slip of a Simple Gas

The flow of a simple gas along a plane surface under the action of tangential temperature gradient is considered. The velocity of thermal slip is calculated by the variational method with account of the effect of surface forces. It is shown that, in some situations, surface forces can substantially affect the value of the thermal slip coefficient.     

Me2ESiMe3 (E = As,N, P) Compounds—Efficient Reagents for Replacement of the Fluorine Atom by Me2E Group in the Complex [(η6-1-F-3,5-Me2C6H3)(η5-C5EtMe4)Rh](CF3SO3)2 >

Russian Journal of Organic Chemistry -     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXVII.1 Effect of Nucleofuge and Solvent of the Relative Rates of Heterolysis of 1-Halo-1-methylcyclopentanes and 1-Halo-1-methylcyclohexanes. Correlation Analysis of Solvation Effects

The effect of solvent ionizing ability on heterolysis rate enhances in the series 1-chloro-1-methylcyclohexane < 1-bromo-1-methylcyclohexane 1-chloro-1-methylcyclopentane < 1-bromo-1-methyl- cyclopentane. The lower sensitivity of cyclohexyl substrates compared with cyclopentyl is determined by conformational effects. Bromides are more sensitive to solvent effects than chlorides because of the stronger polarizability of the C-Br bond.     

Chlorine derivatives of octaorganylsilasesquioxanes

The chlorination of saturated and unsaturated octaorganylsilasesquioxanes proceeds through two pathways, leading to the formation of volatile and nonvolatile products, whose ratio depends on the reaction conditions. The volatile products of the chlorination of R-T₈ (R=C₂H₅ and CH=CH₂) are compounds with the general formula Cl_nR_8–n[SiO_1.5]₈, (n=1–7), obtained independently of the nature of the organic substituent and chlorinating agent. The nonvolatile chlorination products are silasesquioxanes, containing chlorine and chloroalkyl substituents on the atoms of the silicon-oxgyen core. Analysis of the vibrational spectral data indicated that the most significant changes in the molecular vibrational system are made by the halogenation of the silicon-oxygen core Si₈O₁₂.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 446–450, February, 1990.