Some difficulties in the application of the concept of density of states

The problem of defining N(E), the density of states, for molecular systems is discussed. It is shown that a numeric evaluation of N(E) is often only approximate, even for continuous data, and is not well defined for quantized systems. The application of the concept of density of states is discussed, particularly with regard to the RRKM theory of unimolecular reactions. The sum of states, W(E), and density of states curves are evaluated for several harmonic and anharmonic model systems and the results discussed in order to illustrate the foregoing considerations.     

Analyse de la fraction monophénolique des condensats de fumée de cigarettes par association de méthodes chromatographiques

Résumé Les monophénols sont isolés des condensats de fumées de cigarette par chromatographie sur couche mince de Kieselgel G avec un mélange (31) de cyclohexane et d'acétate d'éthyle extraits du support, puis séparé et dosés par chromatographie en phase gazeuse sur colonne capillaire. Le rendement de l;opération est de 80±2% pour le triméthyl 3,4,5 phénol, de 65% pour le triméthyl 2,3,5 phénol. Les teneurs obtenues sont de 8g de phénol, 3g de (para + méta) crésol et 0,5 g de diméthyl 2,6 phénol par mg de condensat. De nombreux autres alkylphénols ont été identifiés.

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Analysis of the monophenolic fraction of tobacco smoke condensates by a combination of chromatographic methods

Summary Monophenols are separated from tobacco smoke condensates by thin-layer chromatography on Kieselgel G using a 31 mixture of cyclohexane and ethylacetate. The monophenolic fraction is recovered from the support and analyzed by GC on a capillary column. The yield is 80±2% for 3,4,5 trimethylphenol and 65% for 2,3,5 trimethylphenol. The concentration determined for phenol, (para+meta) cresol and 2,6 dimethylphenol are 8,3 and 0.5 g per mg of condensate respectively. Numerous other alkyl phenols have been identified.

     

Total synthesis of indole and dihydroindole alkaloids. VII. The total synthesis of isovelbanamine, velbanamine, cleavamine, 18beta-carbomethoxycleavamine and catharanthine.

A synthesis of a variety of nine-membered ring intermediates in the cleavaminevelbanamine series is described. The formation of the penultimate intermediate involves a fragmentation reaction in which the cleavamine system is generated from an appropriate rigid pentacyclic Iboga alkaloid derivative. Thus dihydrocatharanthinol tosylate (VIII) on reaction with triethylamine in refluxing benzene undergoes fragmentation to the 5, 18-seco-diene X. This latter substance is then elaborated in various ways to the desired compounds.     

Etude de la chloration du polychlorure de vinyle en fonction de sa tacticite

Polyvinyl chloride samples of various tacticity have been prepared and photochlorinated in CCl₄ for 4 hr. The chlorination degree correlates directly with the degree of syndiotacticity. Initial PVC with syndiotacticity about 56 per cent, which can be regarded as alternate sequences of syndiotactic and isotactic diads, is quickly chlorinated. The mechanism of chlorine attack on the macromolecula is directly connected with the stereoregularity.     

New method for the synthesis of macrocyclic compounds

A mixture of isomers corresponding to closing of the ring at the 3 and 4 positions of the thiophene ring is formed during intramolecular acylation of 12-(5-methyl-2-thienyl)-lauryl chloride in a homogeneous medium; the reaction proceeds primarily to favor the formation of the isomer with the larger ring (80%). A method for the synthesis of macrocyclic -alkylcycloalkanones by reductive desulfurization of the corresponding bicyclic ketones, which contain thiophene rings, was developed.See Izv. Akad. Nauk SSSR, Ser. Khim., 2228 (1970) for Communication XI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1467–1472, November, 1970.     

Coulometric titration of acids in non-aqueous solvents

Coulometric titrations of mineral acids, sulphonic acids, carboxylic acids, enols, imides and phenols have been carried out in t-butanol or in acetone with electrically generated tetrabutylammonium hydroxide. Either a potentiometric titration or a visual indicator end-point may be used. The amount of acid titrated ranges from 10 to 60 muequiv, and the precision and accuracy of the method are excellent.     

Nitration of Durene and Pentamethylbenzene with Nitronium Salts in Nitromethane and Acetonitrile

Nature and proportions of the products formed in the nitrations mentioned in the title are affected by the process of mixing. Pentamethylnitrobenzene, formed initially in the nitration of pentamethylbenzene, is attacked by a nitronium ion at a position meta to the nitro-group. In the σ-complex formed, loss of a proton from a methyl group leads to production of by-products and release of nitrite ions. The nitrous acid formed is protonated, and water is displaced from the nitrous acidium ion by the anion, PF₆^?, giving the nitrosonium ion which forms a 1:1 symmetric molecular complex with pentamethylbenzene. A similar complex is formed in the reaction between durene and nitronium salts. The results are consistent with the view that no σ-bond is formed between the aromatic compound and the nitrosonium ion.     

Kryoskopische Bestimmung der Aktivitätskoeffizienten von Nichtelektrolytmischungen

Zusammenfassung Es wurde eine Methode entwickelt, welche die Aufnahme von Schmelzkurven von binären Nichtelektrolytmischungen mit einer Genauigkeit von 0,001° (und dementsprechend von etwa 0,00001 im Molenbruch) gestattet. Die Bestimmung der Schmelzpunkte erfolgte an Hand von Erwärmungskurven, die bei konstanter Wärmezufuhr mit einem Thermistor aufgenommen wurden.Die Methode wurde auf die Systeme 1,2,4-Trichlorbenzol-(1)-n-Hexan und Anilin-(1)-Cyclohexan angewendet und sollte hier der Überprüfung und Ergänzung der Daten dienen, die früher aus Dampfdruckmessungen¹ und Messungen der Löslichkeitskurve² abgeleitet wurden. Die Übereinstimmung mit den früheren Resultaten ist bei dem System Trichlorbenzol-Hexan ausgezeichnet, bei dem System Anilin-Cyclohexan annehmbar. Die nun genauer zu bestimmenden lnf ₁/x ₂ ² -Kurven (f _i Aktivitätskoeffizient,x _i Molenbruch der Komponentei) zeigen bei dem Übergang von verdünnter zu konzentrierterer Lösung eine plötzliche Änderung, als ob mit Erhöhung der Konzentration der Komponente 2 eine plötzliche Änderung der molekularen Struktur der Lösung einherginge. Dieser Befund steht zwar mit früheren Beobachtungen^1,2 in qualitativer Übereinstimmung, konnte aber bisher nicht so scharf formuliert werden.Mit 11 AbbildungenAuszugsweise vorgetragen auf der Chemiedozententagung der Chemischen Gesellschaft der Deutschen Demokratischen Republik in Halle (Saale) 24.–26. Juni 1959.     

Basische Metalle. LXIV. Lewis-basische Bis(trimethylphosphan)cobalt-Komplexe mit Indenyl und Trifluormethylcyclopentadienyl als Liganden

Basic Metals. LXIV. Lewis-basic Bis(trimethylphosphine)cobalt Complexes with Indenyl and Trifluormethylcyclopentadienyl as Ligands The half-sandwich type compounds C₉H₇Co(PMe₃)₂ ( 1 ) and (C₅H₄CF₃)Co(PMe₃)₂ ( 6 ) are prepared from CoCl(PMe₃)₃ and C₉H₇Li or TlC₅H₄CF₃, respectively. They behave like metal bases and react with HBF₄, CH₃I (or CF₃SO₃CH₃), I₂, and CH₃COCl by oxidative addition to give the cationic complexes [C₉H₇CoX(PMe₃)₂]⁺ and [(C₅H₄CF₃)CoX(PMe₃)₂]⁺ (X ? H, CH₃, I, COCH₃) which are isolated as the PF₆ salts ( 2–5 and 7–10 ). The ¹HNMR and the IR spectra of the compounds 1–10 are discussed, also in comparison to those of the corresponding cyclopentadienylcobalt complexes.     

Identification of a series of C25-C40 acyclic isoprenoid hydrocarbons in crude oils

The identification of acyclic isoprenoid hydrocarbons in organic extracts of geological samples and particularly in petroleum deserves a great interest from the biological origin of the sedimentary organic matter and the understanding of geochemical processes.