T. Caronna

Nucleophilic character of alkyl radicals—II : Selective alkylation of pyridine, quinoline and acridine by hydroperoxides and oxaziranes

Abstract Homolytic alkylation of pyridine, quinoline and acridine by redox systems is a selective process as regards orientation and reactivity. The synthetic aspects and the mechanism of the reduction of oxaziranes and homolytic substitution are discussed.

Nucleophilic character of alkyl radicals—XIII: Absolute rate constants for the addition of alkyl radicals to acrylonitrile and methyl acrylate

Abstract The absolute rate constants for the addition of alkyl radicals to acrylonitrile and methyl acrylate are determined by evaluating the ratio of ligand-transfer oxidation and addition to the double bond. Secondary alkyl radi c als appear to be more reactive than primary alkyl radicals, despite the less favourable energetics. The classical selectivity : reactivity relationship is reversed owing to the nucleophilic character of the alkyl radicals.

Approaches to the Azahelicene System: Synthesis and Spectroscopic Characterization of Some Diazapentahelicenes

The synthesis and spectroscopic characterization of some diazahelicenes is presented. The synthetic approach varies according to the location of the N-atoms; thus, three different synthetic pathways are used (Schemes 1–3). A description of UV/VIS and of fluorescence and phosphorescence emission is also reported. NMR Spectra show the importance of the distorted backbone of these molecules.

A novel substitution reaction by photoinduced electron-transfer between pyridine derivatives and alkyltin compounds

Abstract Photolysis of pyridine derivatives in the presence of SnBu 4 or Sn 2 Bu 6 leads to butyl derivatives in the α and γ positions. With 2,4-dicyanopyridine ipso-substitution of the cyano groups with the butyl groups exclusively occurs. With 4-cyanopyridine both ipso-substitution and substitution at the 2-position take place. A photo-induced electron-transfer mechanism is suggested.

Photoreactions 0f 4-cyanopyridine with alkenols influence of the medium on the reaction mechanism and photoproducts formation

Abstract Irradiation of 4-cyanopyridine in the presence of 4-penten-1-ol and 5-hexen-1-ol is reported. Hydrogen abstraction from the methylene α to the hydroxyl group in neutral medium and an electron transfer from the double bond in acidified medium account for the photoproducts obtained.

Photoinitiated substitution reactions of 2 and 4-pyridinecarbonitrile with cyclopentene

Abstract The photoreactions of 4 and 2-pyridinecarbonitrile with cyclopentene carried out in acetone or in acetonitrile solutions lead, respectively, to 4-(2 cyclopentenyl)-pyridine 1 and 2-(2 cyclopentenyl)pyridine 2 . From 2-pyridinecarbonitrile a little amount of ketone 3 is obtained.

Photostability of substituted 4-diethylaminoazobenzenes

The stability to visible light of five 4-diethylaminoazobenzenes was investigated in different solvents under various experimental conditions, as well as in solid crystalline form and on dyed poly(ethyleneterephthalate). Though generally exhibiting relatively high photostability, all investigated dyes underwent photodegradation in acetone solution. Two different reaction paths were recognised in this solvent, depending on the nature and position of the substituting groups on the second aromatic ring, both involving the formation and subsequent fragmentation of organic free radicals, as suggested by the strong inhibiting effect of molecular oxygen on the photodegradation rate.

Crystalline organization and bonding of N-perfluoroacylpyridiniumaminides

Abstract N -Perfluoroacylpyridiniumaminides are stable crystalline solids characterized by a potentially useful set of properties. The molecular geometries resulting from the determination of the crystal structures of three members of the series suggest that, due to the presence of the perfluoroalky chains, the electron density on the formally negatively charged nitrogen of the ylide system is reduced. The N–N and the OC–N bonds in the systems are shortened and the whole molecules are stabilized as compared to non-fluorinated N -alkanoylpyridiniumaminides. The packing in the crystals can be qualitatively understood as a compromise between two distinct effects: 1. the tendency to segregate, of the fluorocarbon groups on one hand and the bipyridinium blocks on the other, as in the case of 4b or c , 2. the formation of weak interactions involving the pyridinium hydrogens and the most effective hydrogen bond accepting atoms (i.e. O and N). The latter effect leads to disorder of the perfluoroalkyl chains in 4a . In 4b and c , even at room temperature, a surprisingly ordered arrangement of the segregated perfluoropropyl chains is observed, showing a clear tendency to helicoidal conformation related to fluorine–fluorine repulsion.

Photochemical synthesis and structural properties of high membered thiohelicenes

A general photochemical synthesis of large thiohelicenes containing nine and eleven rings is discussed along with the organisation of racemic thiohelicenes in crystals: heterochiral assembling is dominant except in the nine-ring system where interactions involving terminal ring S atoms favour the segregation of close-packed homochiral molecules in planes.

New photochemical synthesis of transparent conducting polydithieno[3,4-b; 3′,4′-d]thiophene

The preparation of conducting polydithieno[3,4-b; 3′,4′-d]thiophene via photochemical polymerisation leads to a thin film with electrochromic properties in the visible region.