Electrochemically catalyzed cleavage of carbon-carbon bond The intermediate formation of metal—Carbene complexes

This paper descirbes a polarographic method for the determination of the formation constant for the binding of molecular oxygen with several cobalt(II) Schiff-base complexes. The method consists of determining, from the polarographic diffusion current for the reduction of the oxygenated complex, the oxygen partial pressure at which half of the complex is oxygenated. At this point, the partial pressure determined with a Clark-type membrane electrode is equal to the reciprocal of the formation constant, K_oxy, for the oxygenated species. K_oxy values of 0.128, 0.162 and 0.178 Torr^?1 were obtained for the Co(II) SALEN, SALOPH and 3-methoxySALEN complexes, respectively, at 0° C in pyridine. This method can be used to determine K_oxy values as large as 2.0 Torr^?1 with an estimated uncertainty of 5–10%, based on the uncertainty of the oxygen electrode measurement.     

About the limits of existence of α-cluster structure in nuclei

The shape of the d-α coincidence spectrum from the reaction ¹²C(⁶Li, d)¹⁶O(α)¹²C in the region corresponding to the 20.9 MeV 7^? level in ¹⁶O has been measured. Also, measurements of the α-particle elastic scattering excitation functions on ¹²C and ¹⁶O have been made in the regions corresponding to the α-cluster levels found in the (⁶Li, d) reactions. A comparison of the d-α coincidence spectra and excitation functions allows us to draw conclusions about splitting of the α-cluster states and region of their existence.     

4-(1-Haloalkyl)-3-nitrotetrahydrofurans as versatile scaffolds for the synthesis of diversely functionalized tetrahydrofurans

4-(1-Haloalkyl)-3-nitrotetrahydrofurans, which are accessible by tandem oxidative oxa-Michael addition/radical cyclization/ligand transfer reactions, can be processed to diversely substituted tetrahydrofuran derivatives. Selective epimerization at the nitro function provides tetrahydrofuran diastereomers, which cannot be prepared by the tandem process. Intramolecular alkylations furnish interesting bridgehead nitro oxabicyclo[3.1.0]hexane derivatives in high yields. Intermolecular substitution reactions of the halide functions succeed only with nucleophiles, which are not basic enough to trigger intramolecular alkylations. The aryl substituent in 2-aryl-3-nitrotetrahydrofurans can be selectively oxidatively transformed to carboxylic acid derivatives using catalytic Ru(III) and NaIO₄ without affecting the nitro group. Reduction and hydrogenation reactions provide differently substituted 3-aminotetrahydrofuran derivatives depending on the conditions with moderate to good chemoselectivity.     

Oxidative tandem alkoxide conjugate addition to nitroalkenes/radical 5-exo cyclizations—a versatile synthesis of functionalized 3-nitrotetrahydrofurans

Structurally diverse functionalized 4-(1-haloalkyl)-3-nitrotetrahydrofurans were conveniently obtained in moderate to good yield and moderate to very good diastereoselectivity by an oxidative tandem process consisting of conjugate addition reaction of lithium allyloxides to nitroalkenes followed by SET oxidation of the resulting nitronates. This triggers a radical cyclization; ligand transfer from the oxidant provides the products. The influence of the counter ion of the initial alkoxide and intermediate nitronate, the solvent and additives on the outcome of the tandem process was investigated. Optimal conditions for the tandem reactions consist of using butyllithium as the base for deprotonation in DME as the solvent. Cupric halides proved to be the SET oxidants of choice in the tandem reactions. A stereochemical model for the radical cyclization and ligand transfer steps is proposed.     

Some Aspects of Dynamics of Nitrogen-14 Quadrupolar Spin-System

This is a study of the behaviour of nuclear quadrupole resonance (NQR) signals in the “observation windows” of multi-pulse sequence for a nitrogen-14 spin-system. Obtained results revealed steady state (SS) and spin echo (SE) components of the signal. The results contribute to the understanding the dynamic properties of the quadrupolar spin-system.     

Nonlinear equations satisfying the nonresonance condition

In this article, the equation Au ± B(u) = f is studied in a separable Hilbert space H. Here A: H → H is a linear self-adjoint operator with domain dense in H and B: H → H is nonlinear. It is studied when this equation has a solution for any f ∈ H. The results obtained are applied to the problem of periodic solutions of the nonlinear wave equation with homogeneous boundary conditions of the third kind and to elliptic equations. __________ Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 25, pp. 226–248, 2005.     

On the adequacy of modeling the concentration dependences of the activity coefficients for the components of solutions

An analysis of the accepted methods for calculating the activity coefficients for the components of binary aqueous solutions was performed. It was demonstrated that the use of the osmotic coefficients in auxiliary calculations decreases the accuracy of estimates of the activity coefficients. The possibility of calculating the activity coefficient of the solute from the concentration dependence of the water activity was examined. It was established that, for weak electrolytes, the interpretation of data on heterogeneous equilibria within the framework of the standard assumption that the dissociation is complete encounters serious difficulties.     

Periodic Solutions of a Nonlinear Wave Equation with Nonconstant Coefficients

The existence of time-periodic solutions of a nonlinear equation for forced oscillations of a bounded string is proved when the d'Alembert operator has nonconstant coefficients and the nonlinear term has power-law growth.