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February 2, 2018 | Chemistry | By admin | 0 Comments

By Konstantinova E.

Graph illustration of molecular constructions is commonly used in computational chemistry and theoretical chemical researches. Trinajstic famous that the roots of chemical graph concept can be present in the works by means of chemists of 18-19 centuries resembling Higgins, Kopp, Crum Brown. they've got used first chemical graphs for representing molecules. Molecular constructions are represented by means of graphs the place vertices correspond to atoms, and edges to chemical bonds. this type of a graph, referred to as now a molecular graph, is the article of analysis within the idea of standard graphs. despite the fact that traditional graphs don't appropriately describe chemical substances of nonclassical constitution. a considerable trouble of the constitution concept is the inability of a handy illustration for molecules with polycentric bonds. generally polycentric bonds are encountered in organometallic (sandwich-type) compounds, polycyclic conjugated molecules, benzenoid platforms specifically, etc.In 1994 the idea that of a molecular hypergraph, as a mathematical software compatible for modeling the constitution of molecules with polycentric bonds was once brought [46]. major aim of this Lecture Notes is to illustrate merits of an software of hypergraph idea in chemical researches.

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Improvements or circumventions of existing patents, utilizing the same sequence in alternatively derivatized precursors, are listed in Reaction scheme 71. Reaction scheme 71 bose ~x ) X= CHO. CH(OAIkh [201] CONHAIk [192]. J N [192] Reaction scheme 72 o ~CO o Of particularly interest is Reaction scheme 72 for its stereochemical outcome yielding an activated cis-permethric amide 122 and for the utilization of iron pentacarbonyl as a radical starter [203, 205]. The importance of 3,3-dimethylpentenoic acid or its derivatives as the technical pyrethroid key-chemical is reflected in the divers proposals for cheap and technically feasible processes (Reaction schemes 73-78).

Even sugar can be transformed into l-R-chrysanthemic acid [U8] via a multistep procedure. Likewise, optically active pantolactone 78 [119] can be reduced, ketalized, mesylated and later on subjected to cyanide exchange to give 79. Partial repetition of this sequence leads to an optically active precursor 80 for a 1,3-cyclo-elimination to a cis/trans mixture of hydroxy nitrile 81. Interestingly, ex-epimerization with lithium diisopropyl amide is dominated by an absolute configuration at the ~-carbon, yielding the cis isomer 82.

Minute changes in the structure of the amines often prevent the resolution. ~ [77~OH ~N V I H Recently enzymatic (kinetic) resolutions using esterases from the liver [87] or microorganisms [88, 89, 90] aroused interest. For separation of cis/trans racemic mixtures of chrysanthemic acid into pure cis or trans racemates, the lower solubility of cis acid [7], the faster saponification of trans ester [91], the ability of cis acid for intramolecular reactions [92] or the pK-difference:; between cis and trans in connection with phase distribution [93] can be exploited.

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Chemical hypergraph theory by Konstantinova E.

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