Reactivite d'hydrocarbures methylenecyclo-hexaniques—I : Stereochimie de la reaction d'oxymercuration-demercuration

Methylenecyclohexanes, prepared in excellent yield by Corey and Chaykovsky then Cornforth reactions, give on oxymercuration followed by reductive demercuration tertiary alcohols resulting from axial attack by solvent. The attack takes place trans to the substiuent when the latter is at the 2 position. α-Hydroxy or methoxy compounds behave similarly to each other. For acetoxy compounds, the cis alcohols are obtained preferentially, by intramolecular attack of acetoxy group on the mercurinium ion intermediate. The results can be explained satisfactorily on the assumption that the factors inducing stereochemistry are short distance interactions.     

On the Correlation between Ionization Potentials and Excitation Energies,part III: Pyrazine

A recently suggested scheme for relating ionisation potentials (IP) to excitation energies (E) has been applied to pyrazine and 2,6-dimethylpyrazine. The results indicate that in these systems the energy gap (ΔE) between the two lowest lying ¹n,π*-states is significantly smaller than that (ΔIP) between the corresponding ²n-states of the parent radical cations. The values estimated for ΔE on the basis of ΔIP, measurable by photoelectron spectroscopy, disagree with those calculated theoretically but seem to be supported by the experimental evidence available. Since ΔE = ΔIP would normally be expected, the relationship ΔE < ΔIP actually present in these systems is discussed and related to the different shape of the n-MO's involved in the ionization and excitation processes.     

Dienic sex pheromones : Stereoselective syntheses of (7E,9Z)-7,9-dodecadien-1-yl acetate, (E)-9,11-dodecadien-1-yl acetate,and of (9Z), 11E)-9,11- tetradecadien-1-yl acetate by palladium-catalyzed reactions

Pure (7E,9Z-7, 9-dodecadien-1-yl acetate (1), the sex pheromone of Lobesiabotrana, has been prepared in 21.6% overall yield by a reaction scheme involving; (i) the cross-coupling of (E) - 8 - (2 - tetrahydropyranyloxy) -1 - octenyldisiamylborane with 1 - bromo - 1 - butyne, in the presence of a Pd (O) catalyst and base; (ii) the acetylation of the crude product of this reaction; (iii) the (Z)-stereoselective reduction of the obtained conjugated (E)-enyn-1-yl acetate. (E)-9,11-Dodecadien-1-yl acetate (2), a sex pheromone component of Diparopsiscastanea, has been analogously obtained (in 54.3% overall yield) by cross-coupling of (E) - 10 - (2 - tetrahydropyranyloxy) - 1 - decenyl borane with vinyl bromide, in the presence of a Pd (O) catalyst and base, followed by acetylation of the crude product. Compound 2, which was 87.7% chemically pure, was purified by column chromatography over SiO₂-AgNO₃. Chemically pure (9Z, 11E) - 9,11 - tetradecadien - 1 - yl acetate (3), a sex pheromone component of Spodopteralittoralis, has been prepared (in 30.2% overall yield) by reaction of 10 - (2 - tetrahydropyranyloxy) - 1 - decynylamagnesium bromide with (E)-1-iodo-1-butene, in the presence of a Pd (O) catalyst, followed by acetylation of the crude product and by (Z)-stereoselective reduction of the obtained (E)-enyn-1-yl acetate.The stereoisomeric purity of 1, 2 and 3 has been evaluated by glc analysis on glass capillary columns or by reverse phase hplc analysis.     

Dual-flame photometric detector (DFPD) for the simultaneous G. C. determination of P-, S-, Cl-containing organic compounds

Summary The construction and set-up of a dual-flame photometric detector (DFPD) which, through three channel operation, allows the simulatneous selective determination of P-, S-, Cl-containing compounds eluted from a G. C. column is described. For P- and S-containing compounds the molecular emission bands HPO and S₂ at 526 and 394 nm respectively are measured; for Cl-containing compounds, after reaction with In, the InCl band at 360 nm is recorded. Detectability, specificity, linearity as well as mutual interferences are discussed and compared with those of classical GC-detectors as thermionic (TID) and electron capture (ECD). Some practical applications concerning the pesticide residue analysis in animal and vegetable extracts are shown.

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Zwei-Flammen-Photometer-Detektor (DFPD) für die gleichzeitige G. C. Bestimmung von P-, S-und Cl-enthaltenden organischen Verbindungen

Zusammenfassung Der Aufbau und die Justierung eines Zwei-Flammen-Photometer-Detektors, welcher durch 3-Kanal Arbeitsweise eine gleichzeitige selektive Bestimmung von P-, S- und Cl-enthaltenden Verbindungen erlaubt, wird beschrieben. Für P- und S-enthaltende Moleküle werden die Molekül-Linien HPO und S₂ bei 526 bzw. 394 nm gemessen; bei Cl-enthaltenden Verbindungen wird, nach Reaktion mit In, die InCl-Linie bei 360 nm registriert. Nachweisgrenze, Spezifität, Linearität sowie Quereinflüsse wechselseitiger Interferenzen werden diskutiert und mit den entsprechenden Werten klassischer GC-Detektoren wie TID und ECD verglichen. Einige praktische Anwendungen bei der Pestizid-Rückstand-Analyse in Extrakten von Tieren und Pflanzen werden gezeigt.

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Détecteur photométrique à double flamme (DPDF) pour la détermination simultantée des composés organiques contenant du P, S, Cl en CG

Résumé On décrit la construction et la mise au point d'undétecteur photométrique à double flamme («DFPD»=DPDF); celui-ci permet grâce à système à «3 canaux» de déterminersimultanément et sélectivement les substances organiques contenant du P, du S, du Cl, à la sortie des colonnes de chromatographie en phase gazeuse. Pour les substances contenant du P et du S, on mesure l'émission moléculaire correspondant aux bandes dûes à HPO et S₂ (526 et 394 nm. respectivement); pour les composés chlorés, on mesure l'émission correspondant à la bande due à InCl (360 nm.) après réaction avec l'Indium des gaz brulés. Les problèmes relatifs à la limite de détection, à la specificité et à la linéarité de la réponse en fonction de la quantité de substance injectée, ainsi qu'aux interactions entre substances détectées, sont discutés et les rultats obtenus sont compar avec ceux fournis par les détecteurs classiques: thermo-ionique («TID»=DTI) ou à capture d'électrons («ECD»=DCE). Quelques applications pratiques dans le domaine de l'analyse des résidus de pesticides dans des extraits d'origine animale ou végétale sont données comme exemples.