X-ray structural investigation on alkaloids V. Crystal and molecular structure of sibiricine

Summary A complete x-ray structural investigation of the spirobenzy1isoquinoline alkaloid sibiricine in the form of the base has been carried out. The bond lengths and valence angles are the usual ones.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 752–758, November-December, 1978. Original article submitted July 4, 1978.     

Stereochemistry of terpenoid coumarins. Crystal and molecular structure of samarcandin

The absolute configuration of samarcandin has been established on the basis of the results of a complete X-ray investigation. The absolute configurations of conferol, moscharol, badrakemin, and coladonin, and the absolute configurations of feshurin, nevskin, and isosamarcandin have been refined.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek, SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 184–190, March–April, 1985.     

Complexes of the porphyrins of Karazhanbass petroleum with transition-metal ions

The possibility and prospects of the use of petroleum porphyrins isolated from Karazhanbass petroleum for the synthesis of complex compounds of the transition metals has been shown.Institute of the Petroleum and Natural Salts, Academy of Sciences of the Kazakh SSR, Bur'ev. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 621–624, September–October, 1990.     

Collinear cluster tripartition as sequential binary fission in the <Superscript>235</Superscript>U(n<Subscript>th</Subscript>, f ) reaction

The mechanism leading to the formation of the observed products of the collinear cluster tripartition (CCT) is carried out within the framework of the model based on the dinuclear system concept. The yield of fission products is calculated using the statistical model based on the driving potentials for the fissionable system. The minima of potential energy of the decaying system correspond to the charge numbers of the products which are produced with large probabilities in the sequential fission (partial case of CCT) of the compound nucleus. The realization of this mechanism supposes the asymmetric fission channel as the first stage of sequential mechanism. It is shown that only the use of the driving potential calculated by the binding energies with the shell correction allows us to explain the yield of the true ternary fission products. The theoretical model is applied to research CCT in the reaction ²³⁵U(n _th, f). Calculations showed that the heavy products of two fission channels of ²³⁶U^*, ⁸²Ge^* + ¹⁵⁴Nd^* and ⁸⁶Se^* + ¹⁵⁰Ce^*, can undergo sequential fission forming the CCT products ⁷⁰Ni, ^{74, 76}Zn, ⁸⁰Ge and ⁸⁴Se with relatively large probabilities which can be observed in coincidence with corresponding partner nucleus. The obtained results can explain some of the observed CCT products Ni and Ge in coincidence with the Ge and Se isotopes in the experiments of the FOBOS group in Joint Institute for Nuclear Research.     

Basic distinctions between cold- and hot-fusion reactions in the synthesis of superheavy elements

Superheavy elements (SHE) of charge number in the range of Z = 106–112 were synthesized in so-called cold-fusion reactions. The smallness of the excitation energy of compound nuclei is the main advantage of cold-fusion reactions. However, the synthesis of SHEs of charge number in the region of Z ≥ 112 is strongly complicated in cold-fusion reactions by a sharp decrease in the cross section of a compound nucleus formation in the entrance channel because of superiority of quasifission in the competition with complete fusion. Two favorable circumstances contributed to the success of the experiments aimed at the synthesis of the Z = 113–118 elements and performed at the Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research: large cross sections for the production of a compound nucleus, which are characteristic of hot-fusion reactions, and an increase in the fission barrier for nuclei toward the stability island. The factor that complicates the formation of a compound nucleus in cold-fusion reactions is discussed.