π-Electron hyperconjugation in organic molecules and ions

The extent of energetic stabilization by alkyl groups with -electron systems via hyperconjugation is investigated theoretically by MINDO molecular orbital calculations. In neutral hydrocarbons, this stabilization represents about 4 % of the effective C-C bond energy, and is additive in the number of alkyl groups present. Calculations for conjugated, polar, and ionic molecules are also discussed.

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Zusammenfassung Das Ausma\ der energetischen Stabilisierung von -Elektronen-Systemen mit Alkylgruppen durch Hyperkonjugation wird theoretisch durch MINDO-MO-Berechnungen untersucht. In neutralen Kohlenwasserstoffen betrÄgt diese Stabilisierung etwa 4% der effektiven C-C Bindungsenergie und ist additiv entsprechend der Zahl der vorhandenen Alkylgruppen. Berechnungen für konjugierte, polare und ionische Moleküle werden ebenfalls diskutiert.

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Résumé La méthode des orbitales moléculaires MINDO est utilisée pour calculer le degré de stabilisation par hyperconjugaison entre des groupements alkyles et des systèmes d'électrons . Dans des hydrocarbures neutres cette stabilisation représente environ 4% de l'énergie effective de la liason C-C; elle est additive par rapport au nombre de groupements alkyles. On discute aussi des calculs effectués pour des molécules conjuguées polaires ou ioniques.

     

Studies in the benzazole and naphthazole series. VIII. Reaction of 2-hydrazinonaphth[1, 2-d]imidazole and its 1- and 3-methyl derivatives with carbon disulfide

When heated with carbon disulfide in pyridine 2-hydrazinonaphth[1, 2-d]imidazole yields S-triazolo[4, 3-b]-naphth[1, 2-d]imidazole-3-thione. Kinetic and not steric factors determine the formation of this compound. Its trans-angular structure is demonstrated by the agreement between its UV spectrum and that of 11-methyl-S-triazolo[4, 3-b]naphth[1, 2-d]imidazole-3-thione, prepared from 1-methyl-2-hydrazinonaphth[1, 2-d]imidazole and carbon disulfide, as well as by the identity of their methylation products. Methyl iodide methylation, in the presence of sodium methoxide, of S-triazolo[4, 3-b]naphth[1, 2-d]imidazole-3-thione, like that of S-triazolo[4, 3-a]benzimidazole-3-thione, takes place stepwise. First the methyl group adds to the nitrogen atom of the imidazole ring, and only then to the thiol group of the triazole ring.For Part VII see [3].     

Synthesis of 1,4-dihydropyridines having an N-alkylpyridinium substituent at the 4-position and their affinity towards liposomal membranes

There has been synthesized a series of 1,4-dihydropyridines having an N-alkylpyridinium substituent at position 4 with a varying length of hydrocarbon chain. Their affinity to model (liposomal) membranes has been studied. It was found that this affinity increased with lengthening of the hydrocarbon chain on the Npyridinium substituent at the 4-position of the 1,4-dihydropyridine ring. However, lengthening of the hydrocarbon chain in the 3,5-ester groups of the 1, 4-dihydropyridine ring led to a decrease in the binding to the liposome when a 4-(N-hexadecylpyridinium) substituent was present.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1112–1117, August, 1995. Original article submitted June 6, 1995.     

Topological analysis of the structure-mesomorphous property ralationship

The use of topological indices to reveal the relationship between molecular structure and mesomorphous properties is discussed. Mathematical models for classification of mesophase types are proposed. The effect of molecular structure and attractive ability on phase transition temperatures is described. Examples of using correlation equations to predict the properties of 2,5-disubstituted 1,3-dioxanes are given. A. V. Bogatskii Physicochemical Institute, Ukrainian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 35, No. 4, pp. 53–60, July–August, 1994. Translated by L. Smolina     

Purification of 3-ethoxycarbonylquinuclidine and its conversion to 3-quinuclidinecarboxylic acid and 3-quinuclidinylmethanol

3-Ethoxycarbonylquinuclidine obtained by the Grob method is a mixture of 3-ethoxycarbonyl-1-azabicylo-[2.2.2]- and, according to ¹³C NMR data, 5-ethoxycarbonyl-5-azatricyclo[3.2.1.0^2,7]octanes (1621). 3-Ethoxy-carbonylquinuclidine was purified by recrystallization of the hydrochloride, hydrolyzed by water to 3-quinuclidinecarboxylic acid, and reduced by LiAlH₄ to 3-quinuclidinylmethanol.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, 1509–1512, November, 1992.     

Complex study of nickel skeleton catalysts: V. Study of novel non-pyrophoric nickel skeleton catalysts by derivatograph

The structure and properties of non-pyrophoric skeleton catalysts prepared from NiSi, NiAlSi, NiMg and NiZn alloys have been studied—apart from other thermal methods—by means of the derivatograph.Our experimental results have contributed to the explanation of the non-pyrophoric behaviour of these catalysts. We demonstrated that the desorption of the hydrogen content in our catalysts is not accompanied by the oxidation of active nickel. This oxidation takes place only at higher temperatures, above 200°C, at a rate proportional to the amount of active nickel.Other constituents of the catalysts (adsorbed water, hydroxide content) were also determined from the experimental data. The outstandingly high Mg(OH)₂ content of the NiMg catalyst indicates that its structure is dissimilar: Mg(OH)₂ also acts as support for the catalyst.     

Isotope gas analysis of tritium-labelled organic compounds based on pyrolytical decomposition

Summary A procedure has been developed for the activity measurement of tritium-labelled organic compounds in the gas phase. The organic compounds are pyrolysed in hydrogen carrier gas at 1150° and the decomposition products are swept through a carbon packing in accordance with the principle of the oxygen determination developed byUnterzaucher andBürger. The radioactive gas mixture obtained from the sample is swept by the hydrogen carrier gas flowing continuously through the reactor into a proportional counter tube, after the addition of propanebutane counter gas. By closure of the counter tube at a suitable moment, the radioactive gas is quantitatively trapped in the counter tube. The activity is measured in the limited proportional region. No memory effect occurs. The preparation of the sample requires 12 minutes; the relative standard deviation of analysis is <0.5%.

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Zusammenfassung Ein Verfahren zur Aktivitätsbestimmung bei tritium-markierten organischen Verbindungen in der Gasphase wurde ausgearbeitet. Die organischen Substanzen werden in Wasserstoff als Trägergas bei 1150° pyrolysiert. Die Zersetzungsprodukte werden wie bei der Sauerstoffbestimmung nachUnterzaucher bzw.Bürger über eine Kohleschicht geleitet. Das radioaktive Gas-gemisch aus der Probe gelangt mit dem kontinuierlich strömenden Trägergas in ein Proportionalzählrohr, nachdem Propan-Butan-Zählgas zugesetzt wurde. Man schließt das Zählrohr im richtigen Augenblick, um das radioaktive Gas quantitativ zu erfassen. Die Aktivität wird im Proportionalbereich gemessen. Ein Memory-Effekt tritt nicht auf. Die Vorbereitung der Probe beansprucht 12 Minuten. Die relative Standardabweichung ist kleiner als 0,5%.

     

Cyclophosphamides from aminosugars and aminonucleosides

Condensation of bis-(2-chloroethyl)phosphoramidic dichloride with 3′-amino-3′-deoxy-N,N-dimethyladenosine afforded the 2′,3′-cyclicphosphorodiamidate (III). By an improved synthesis, methyl 3-amino-3-deoxy-β-D-ribofuranoside was obtained as a model compound for conversion to the analogous 2,3-cyclicphosphorodiamidate (XII). Existence of the latter as two diastereomers due to phosphorus asymmetry was shown by nmr analysis, using comparison with the 5-(O-p-nitrobenzoate) (XIII) as a basis for assignments.     

Synthesis and optical properties of nanohybrids in the system constituted by silica and lanthanide phosphoramide complexes

Sol-gel process of hydrolytic polycondensation of tetramethoxysilane with trimethoxysilyl derivatives of lanthanide phosphoramide complexes was studied in order to obtain photoluminescent organic-inorganic hybrid materials. Original Russian Text N.N. Khimich, Yu.L. Zub, L.A. Koptelova, T.S. Mashchenko, E.P. Troshina, M.G. Voronkov, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 11, pp. 1789–1794.     

Synthesis of 3-imino and 3-ylideno derivatives of 4-fluoro-5-polyfluoroalkyl-1,2-dithiolenes

Reactions of 4-fluoro-5-polyfluoroalkyl-1,2-dithiol-3-thiones with hydroxylamine and hydrazines occur with replacement of the thiocarbonyl by imino group affording oximes and hydrazones respectively. N-Alkyl-and N-aryl-3-imino-1,2-dithiolenes formed in reactions of 3-chlorothio-1,2-dithiolium salts with primary alkyl-or arylamines. 3-Chlorothio-1,2-dithiolium salts react with compounds possessing an active methylene group yielding 3-ylideno derivatives of 1,2-dithiolenes.