The fractional derivative expansion method in nonlinear dynamic analysis of structures

Nonlinear Dynamics - The history of formulation of the efficient method for studying the nonlinear dynamic response of structures, damping features of which depend on natural frequencies of...     

Reaction of methyl-4-methylene-2,3-<Emphasis Type="Italic">O</Emphasis>-isopropylidene-β-D-ribofuranoside with <Emphasis Type="Italic">N</Emphasis>-bromosuccinimide in aqueous tetrahydrofurane

Methyl-4-methylene-2,3-O-isopropylidene-β-D-ribofuranoside prepared from D-ribose reacted in a system NBS-THF-H₂O to give a mixture of stereoisomeric products of regioselective bromohydroxylation of a double bond. The reaction involved a hydrolysis of the glycoside bond, but the acetonide protective group was retained. The mechanism of the selective hydrolysis originating from the ring-chain tautomerism of bromohydrins obtained was proved by the ¹H NMR spectra of the steroisomeric methyl-5-deoxy-5-bromo-4-hydroxy-2,3-O-isopropylidene-β-D-ribofuranosides. By crotonic cyclization of the formed masked 1,4-dicarbonyl compounds at heating in benzene in the presence of neutral Al₂O₃ a new chiral cyclopentenone block, 2-bromo-4,5-isopropylideneoxycyclopent-2-en-1-one, was obtained in a low yield.     

Synthesis of enantiomeric (+)- and (-)-6-(1-methylethylidene)-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]furan-1-ones

Baeyer-Villiger oxidation of racemic [2 +2 ]-cycloadduct derived from dichloroketene and dimethylfulvene gave 3,3-dichloro-6-(1-methylidene)-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]furan-2-one, and opening of the lactone ring in the latter with (+)-α-methylbenzylamine produced diastereoisomeric amides which can be readily separated by chromatography on silica gel. The subsequent lactonization and reductive dechlorination afforded enantiomeric (?)- and (+)-6-(propan-2-ylidene)-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]-furan-1-ones.     

Synthesis of thiamono- and thiabicyclanes from sodium sulfide and methanethiolate

1-[5-Acetyl-3-(methylthiomethyl)tetrahydro-3-thiopyranyl]-1-ethanone was obtained by the interaction of sodium sulfide and sodium methanethiolate with formaldehyde and acetone. The intramolecular crotonate condensation of the product leads to 4-methyl-1-methylthiomethyl-7-thiabicyclo[3.3.1]non-3-en-2-one. The participation of 3-methylthiomethyl-3-buten-2-one in the formation of a thiamono-cyclane is clarified. A probable scheme for the conversions is proposed.     

The microscopic theory of pre-equilibrium decay and the photoproton spectra for medium nuclei

The paper deals with the photonucleon energy spectra for two branches of the giant resonance (T _< andT _>) on the basis of the microscopic theory of the pre-equilibrium decay. The first stage of the reaction is described by the wave function obtained by matrix diagonalization based on particle-hole configurations (T _< andT _>). The densities of the intermediate complex statesJ = = 1^– (T _< andT _>) are calculated with the Saxon-Woods potential. Specific calculations have been made for the nuclei of⁶⁰Ni and⁹⁰Zr.     

Analytical folding-potentials and heavy-ion interactions

The angular distributions of neutrons produced in the (γ, n) reaction are reported for the separated isotopes²⁰⁶Pb and²⁰⁸Pb. The experiment made use of highly chromatic photons generated by neutron capture on nickel and chromium in the core of the McMaster Nuclear Reactor, and a high resolution³He detector. Photoneutron spectra were recorded at 7 angles between 20° and 160°. The results were used to infer the extent of photon multipole mixing between 7 and 11 MeV within the framework of the statistical collective model. The existence of M1 strength could not be confirmed but multipole mixing, most likely E2∶E1 was found at all energies. Estimates of the ratio of E2 to E1 strength is given for all photon energies investigated for both lead isotopes.     

On the nuclear interaction potential in the reactions with heavy ions

The interaction potential of heavy ions⁴He,⁶Li,¹²C and¹⁶O is constructed in the folding model. The density distribution of nuclear matter for these nuclei is calculated in the framework of the hyperspherical function method. For the calculation of the folding potentials we have employed the Skyrme nucleon-nucleon forces. The influence of several effects on the results of calculations is studied: the role of the three-body forces of the nucleon-nucleon interaction, dependence of the folding potential on the mass numbers of the colliding nuclei and the possibility of observing the monopole resonance in the ion inelastic scattering. Using our folding potential as a real part of the optical potential we have calculated the differential cross section of elastic scattering of⁶Li from¹²C at laboratory energy of lithium ionsT _L =90.0 MeV. Reasonable agreement with experiment is obtained.     

Stereochemical Aspects of the Beckman Rearrangement of Oximes of Levoglucosenone and Its Dihydro Derivative. Enantioselective Synthesis of (+)-γ-Pelargonolactone

Regiospecific C⁵5 -halogenation with retention of configuration occurred upon Beckman fragmentation of levoglucosenone oxime using SOCl₂ or PBr₃. On the other hand, the oxime of its dihydro derivative gave under these conditions the C⁶ - substitution product. A stereoselective synthetic scheme for (+)--pelargonolactone, an attractant for the rice and corn weevils Sitophiltus zeamais, was developed from the fragmentation product of levoglucosenone oxime.