A. Lablache-Combier

Mechanism of the photochemical substitution of 6-membered ring monoazaaromatic compounds by methanol in neutral and HCl acidified medium

Abstract 6-Membered ring monoazaaromatic compounds such as pyridine, quinoline, 4-methylquinoline, isoquinoline and 9-phenylacridine are converted to the corresponding semiquinone radicals when irradiated in methanol acidified with HCl, ether or neutral methanol. In a neutral medium the hydrogen photoabstraction occurs from an nπ* excited state by a monophotonic process, but in methanol acidified with HCl, the photoreaction corresponds to a biphotonic process. In this case the photoreaction involves an electron transfer from methanol to a protonated upper excited triplet state of the solute (Scheme 2, path 2).

Biosynthesis of Pr toxin from [1,2-13C]acetate: occurrence of induced 13C13C coupling

Abstract The biosynthesis of PR toxin was studied by incorporation of [1,2- 13 C]acetate. The biosynthesis of the eremophilane skeleton of PR toxin follows th

Reductive photocyclization of benzo[b]furans and their analogs

Abstract The UV irradiation of substituted 2,3-diphenylbenzo[b]furans and of 2,3-diphenyl-5-t-butylfuran in n-propylamine gives 1,4-dihydro derivatives of the corresponding aromatic cyclized compounds. This reaction does not involve a photoreduction. It can be concluded from deuterium labelling experiments that H atoms of the alkyl chain of n-propylamine are incorporated in the product. When the solvent is not an unhindered primary amine, only totally aromatic photocyclized products are obtained. It is proposed that hydrogens eliminated during formation of the isolated compounds are released in a reductive form and not as radicals. This is supported by the fact that acenaphthylene is reduced when irradiated in n-propylamine together with 2,3-diphenylbenzo[b]furan under conditions which do not promote, photoreduction. This seems to be a general finding in that the irradiation of stilbene in n-propylamine to acenaphthylene is the same as that of 2,3-diphenylbenzo[b]furan.

Study and characterization of tautomeric triazolium ylids

The presence of two tautomeric forms in equilibrium for some triazolium ylids has been revealed by nmr spectroscopy and confirmed by trapping with picryl chloride

Synthesis and properties of photoreactive polysiloxanes containing pendant functional groups

Functional polysiloxanes containing photo-reactive pendant groups were prepared by multi-step modification of silicone copolymers containing methylhydrosiloxanes units. A first method based on the platinum Catalyzed hydrosilylation of vinylsilyl terminated photoreactive esters allowed to prepare liquid silicone polymers containing photo-dimerizable esters. Another method based of the esterification of pendant epoxy groups previously grafted on the silicone main chain was found as a general and very powerful alternative route to prepare photo-reactive polysiloxanes. The method has been applied to synthesize polysiloxanes containing various functional side-groups such as dimerizable esters, aromatic carbonyl compounds or dyes which possess properties of photochemical interest. The reactivity, the ability to be photosensitized as well as some practical properties of different photo-crosslinkable polysiloxanes modified either by cinnamic, furacrylic or a cyano p styrylacrylic ester groups were examined. A kinetic investigation of the reactivity of the polysiloxane-bound dimerizable chromophores allows to point out the effect of the silicone matrix in comparison with more classical hydrocarbon pho topolymer 8.

The solvation of twisted intramolecular charge transfer fluorescent states by alcohols

Abstract The solvent-induced shift of the emission maximum of 3-(α-naphthyl)-benzo[b]thiophen was measured in a number of solvents. The correlation of the apparent specific solvation by alcohols with the ET(30) parameter is interpreted in terms of the organization of solvent molecules around the hydrophobic solute. An alternative correlation using the dipole moment of the solvent is more suitable for such solutes.

Photoreduction de la benzophenone par des phtalimidines et des dihydro isoquinolones: Etude chimique par RMN PNIC

Benzophenone is photoreduced by pthalimidines and dihydro isoquinolones. The hydrogen atom α to the nitrogen atom is abstracted and radical coupling leads to adducts. CIDNP studies of these adducts show inversion of polarisation for the adduct on the N-alkyl chain when the nitrogen is bound to a benzylic methylene. This inversion is explained by considering that the radical on the N-alkyl chain derives from the radical on the ring.

FORMATION OF SEMIQUINONE RADICALS BY ULTRAVIOLET IRRADIATION OF PYRIMIDINES IN METHANOL

Abstract—Ultraviolet irradiation of pyrimidine and 4‐ and 5‐methylpyrimidine in methanol at 113 K gave the corresponding semiquinone radicals in a monophotonic process. It is likely that this process involves an n* triplet state of the photoexcited pyrimidines.

Solvent and temperature influence on the fluorescence spectrum of 6-amino-5-methyl-2,3-diphenylbenzo[b]furan

Abstract 6-amino-5-methyl-2,3-diphenylbenzo[b]furan (ABF) exhibits a strong fluorescence in the near U V and visible regions. The effects of temperature and solvent on the fluorescence spectrum have been the object of careful study. Both solvent polarity (18 solvents have been used) and temperature variations (from 77 to 473 K) should have an effect on the conformations of the excited state of ABF by deformation of the polycyclic molecular frame. Eleven of these conformations have been highlighted whose fluorescence maxima differ over a range of about 500 cm -1 (1.4 kcal/mol), a value of the same order as the energy of deformation of a benzenic or a furanic ring, as shown by IR spectra. Very important solvatochromic effects have been observed at room temperature, almost 3500 cm -1 in highly polar solvents compared to nonpolar ones. Similarly, thermochromic effects are also large (1000 cm -1 for solutions in nonpolar solvents as compared to 2500 cm -1 for the ones in polar solvents) so, the data obtained so far must be only slightly affected by the current experimental errors.

Cycloaddition reaction of 1,2,4-triazolium phenacylides with cinnamic esters

Cycloaddition regio- et stereospecifique conduisant aux aroyl-5 aryl-1 phenyl-6 tetrahydro pyrrolo [1,2-b]-s-triazolecarboxylates-7. Etude RMN 1 H, RMN 13 C, analyse DEPT