Effet de longueur d'onde et controle par la geometrie de l'etat fondamental de la photoisomerisation de derives de l'hexatriene-1,3,5

Irradiations at different wavelengths (313, 254, 229 and 214 nm) of the 4 geometric isomers of 5-phenyl-1,3,5-heptatriene show that the photochemical behaviour of these trienes is mainly controlled by their ground state equilibrium.     

Processus concurrents de photoisomerisation d'hexatrienes polymethyles: effet de longueur d'one

The ground-state conformer composition is shown to play a determining role in the orientation of the photochemical reactions of two hexatrienes. A pronounced wavelength effect is observed for Z-2,6-dimethyl-1,3,5-heptatriene; photocycloaddition leads to a bicyclo[3.1.0]hexene and [1,5] sigmatropic hydrogen migration occurs from an s-cis-s-trans conformation preferentially excited by longer wavelength light, whereas the Z-E interconversion is predominantly observed as a result of excitation of the s-trans-s-trans conformation by shorter wavelength light.     

Sur la reactivite des organomagnesiens derivant de l'addition d'organomagnesiens allyliques sur l'isoprene

Contrary to a recent report, it is shown that allylic Grignard reagents prepared by treating allylic Grignard reagents with isoprene and a catalytic amount of Cp₂TiCl₂ react normally with carbon dioxide and carbonyl compounds: a complete allylic rearrangement is observed.     

Transposition des oxirannes-ethanols par l'intermediaire d'alcoxyetains. Influence de la configuration de l'oxiranne

The transposition of oxirane-ethanols, through alkoxytin compounds, into oxetane-2-methanols and/or oxolan-3-ols (tetrahydrofuran-3-ols) is dependent upon the oxirane configuration. Cis configuration is more suitable for the formation of the smallest ring. Steric hindrance is not sufficient enough to explain the results.     

Etude theorique de la cycloaddition de l'ozone sur l'ethylene

A theoretical study of the cycloaddition of ozone on ethylene has been carried out by the LCAO-SCF-MO method. The potential energy hypersurface for the reaction has been investigated and the electronic and energetic properties of the transition state have been determined.     

Syntheses d'oxazolidines substituees par l'adamantane et de nitroxydes oxazolidines stables derives de l'adamantane

Adamantane oxazolidine derivatives have been prepared. The corresponding mono and biradicals have molecular shapes well suited to the study of the motion anisotropy in solution.     

Etude de l'action de l'ion fluor sur la laquethorium-spadns

The reaction of fluoride with thorium—SPADNS lake was studied in detail with particular reference to the effects of pH and media. Two methods for the determination of microgram amounts of fluoride based on the reaction are described. The spectrophotometric method developed is more suitable for routine use, but the colorimetric titration method is less sensitive to the effect of large amounts of electrolyte.     

Effet α. influence de la substitution sur l'exaltation de reactivite d'oximes vis-a-vis de l'acetate de p-nitrophenyle

Kinetic measurements show the relation between the magnitude of the “α effect” exhibited by trifluoromethyloximate anions RR'C=N-O^? and the electron attracting properties of the substituents. Indeed, the reactivity enhancement which is observed for α-trifluoromethyloximes is similar to that found in earlier studies of α-hydroxyiminoketones. This characteristic behaviour is no longer observed for oximes bearing an electron releasing substituent at the α-position of the hydroxyimino group. On the basis of sodium oximate molecular orbital energies the “α effect” induced by electron attracting substituents appears to depend on both the interactions of nitrogen and oxygen lone pairs of electrons and the lowering of the π^* vacant orbital thus favouring a secondary interaction between the π^* anion orbital and the π orbital of p-nitrophenylacetate carbonyl group.     

Reaction d'un thiolate de molybdene sur l'hexafluorobutyne

Bis(methyl)disulphide and the organometallic compound {(Cp)Mo(CO)₃}₂ in low oxidation state under photolysis give especially with the hexa-fluorobut-2 yne a 18-electron olefin complexe {(Cp)Mo(CO)₃(CF₃C₂CF₃SCH₃)}. The new compounds are reported and the reaction discussed.     

Influence des solvants sur la copolymérisation de l'acrylamide avec l'acrylonitrile

The copolymerization of acrylamide with acrylonitrile was investigated in various solvents, which can be put into three groups according to their influence on molecular associations; (1) solvents autoassociated by hydrogen- bonds (acetic acid, methanol, water, dimethylformamide); (2) polar solvents which can associate with the NH group of acrylamide (acetonitrile, dioxane, acetone); (3) inert solvents (toluene, benzene, hexane). The reaction kinetics and the compositions of the copolymers are different for each group of solvents. The composition of copolymers formed in solvents of group 1 vary widely, depend- ing on the solvent. Copolymers formed in all solvents of group 2 have the same composition which is that of copolymers formed in bulk. The amount of acrylamide is highest in copolymers formed in inert solvents of group 3. Such parameters as the degree of conversion, the reaction temperature, the mode of initiation and the extent of dilution only slightly affect the composition of copolymers. Homopolymerizations of acrylamide and acrylonitrile were investigated in all solvent used.The results suggest that the effects of solvents on the copolymerization of acrylamide with acrylonitrile are consequences of the various modes of molecular association of acrylamide. The solvents affect the equilibrium between auto- association of acrylamide and its association with solvent and thereby affect the reactivity of the monomer.     

Influence de la solvatation par le tert-butanol sur la structure et la reactivite de l'enolate de potassium de l'acetylacetate d'ethyle en presence de couronne ou de cryptand. etude par spectrometrie infra-rouge et cinetique

The structure and the nucleophilic reactivity of crowned (18-crown-6) or cryptated {cryptand (2.2.2)} potassium ethyl acetoacetate enolate have been compared in tert-butanol and in DME (or THF). In the protic solvent tert-butanol, the crowned and the cryptated potassium enolate species both exist as loose ion pairs in which the enolate anion, strongly hydrogen-bonded to the solvent, is in a “transoid” (non chelating) conformation. Both species show similar reactivities towards alkylating agents but completely different reactivities are observed in aprotic weakly dissociating media (THF, DME). In contrast to what is observed in tert-butanol, the cryptated species and the crowned species have very different nucleophilic reactivities in THF or DME; in those solvents only the cryptated species retains a loose ion pair structure; the crowned species is a contact ion pair in which the enolate anion chelates the potassium cation. The solvation of this crowned chelate species by tert-butanol has been demonstrated in binary mixtures of solvents (C₆D₆-t-BuOH, THF-t-BuOH). The oxygen basicity of the enolate anion is very different in the crowned chelated ion pair compared with the cryptand separated ion pair.     

Synthese de derives de la tobrosamine par addition d'acide hydrazoique sur un systeme enonique dans la serie hydrate de carbone

Derivatives of a new diaminotrideoxy-d-ribo-hexopyranose, a component of the antibiotic tobramycin, have been prepared by addition of the elements of hydrazoic acid to the α, β-unsaturated ketone 8. After 5 min only the kinetically favored product 13 was observed, which is gradually transformed into the thermodynamically more-stable substance 20. The equilibrium mixture after 5 hours contained d-erythro and d-threo isomers 20 and 13 in the ratio 6:4 The d-erythro azide 20 was converted into the derivatives of di-N-acetyl tobrosamine.     

Etude theorique de la cycloaddition de la nitrone sur l'ethylene

A theoretical study of the concerted 1,3-dipolar cycloaddition of nitrone on ethylene has been carried out by the LCAO-SCF-MO method. The potential energy hypersurface for the reaction has been investigated and the characteristics of the transition state have been determined.