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The Reversible Addition-Fragmentation chain-Transfer (RAFT) synthesis of poly(glycidyl methacrylate) (PGMA) copolymers followed by the post-polymerisation treatment with morpholine allows the rational design of amphiphilic block copolymers that are capable of efficiently dispersing single walled carbon nanotubes (SWCNTs) in aqueous media, as shown by comparative photophysical characterisation and AFM analysis.

This paper is aimed at providing an overview of our studies on the title compounds as spin trapping agents, and at emphasising the links between purely cognitive, academic research and industrial applications. Phosphoryl- and thiophosphoryl-dithioformates exhibit a comparable and interesting spin trapping ability, their efficiency being analogous to that of some aromatic thioketones. The spectral hyperfine structure may provide valuable information on the nature of the trapped radical but the phosphorus hfs constant cannot be used as an useful indicator. Thionformates are less efficient spin traps than the corresponding dithioformates, being inert towards stabilised radicals such as benzyl or relatively hindered radicals as tert-butoxyl. In no case could spin adducts to thiolformates be detected, this being an indication that their carbonyl group is significantly deactivated with respect to that of organic and organometallic ketones. Because of their ability in trapping either alkyl or alkoxy radicals both kind of dithioformates were exploited as stabilisers in the processing of such polymers as polypropylene, but their outstanding performance could not compensate for some organoleptic drawbacks that were intrinsic of the thiocarbonyl function. A much more promising application of dithioesters is instead their use as RAFT chain transfer agents in the controlled polymerisation of styrene. Preliminary experiments with benzyl diethoxyphosphoryldithioformate have afforded polystyrene with a polydispersity as low as 1.17, but further studies are needed to fully elucidate the RAFT-polymerisation mechanism and to optimise its outcome.

The addition of silyl and germyl radicals to a series of substituted cyclopentenones and cyclohexenones has been investigated using EPR spectroscopy. At low temperatures the 3-position is the preferred site for addition unless it is substituted or sterically hindered in which case addition occurs at the carbonyl oxygen. The latter process is also favoured at higher temperatures but no evidence has been obtained for either addition at the 2-position or for an intramolecular migration following initial attack at the 3- or 2-position.

Electron paramagnetic resonance has been used to characterise free radicals formed by the reaction of photochemically generated tert-butoxyl radicals with a range of methyl substituted cyclopentenones and cyclohexenones. The spectra have been interpreted using computer analysis and simulation and assigned to cyclic allylic and alkyl radicals formed by abstraction of a hydrogen atom. The 1-oxocyclohept-2-en-4-yl radical derived by abstraction of bromine from 4-bromocyclohept-2-enone exhibits a temperature dependent EPR spectrum attributed to ring inversion.

The addition of a variety of radicals to triphenylmethyl l, allyl 2, benzyl 3 and but-3-enyl (diethoxyphosphoryl)dithioformate 4 has been investigated by EPR spectroscopy. Reactions with the first substrate always led to displacement of the triphenylmethyl radical; release of the allylic or benzylic moieties from 2 and 3 was observed above 243 K under photolytic conditions, while at lower temperatures or in the dark the adducts resulting from thiophilic addition of the radicals were detected. The weak EPR spectra detected when reacting dithioformates 1–4 and methyl(diethoxyphosphono)dithioformate 5 with Grignard reagents are attributed to the radical anions of the starting compounds and to their ion pairs with magnesium cations.

3,5-Di-tert-butylthiobenzoyltriphenylsilane (DBTBTPS) has been synthesized and tested as a spin trapping agent for electron spin resonance studies. Upon reaction with a variety of radicals of different nature inside the cavity of the ESR spectrometer, DBTBTPS leads to the observation of rather persistent spectra which in nearly all cases allow the unambiguous identification of the trapped species. DBTBTPS is somewhat less stable than thiobenzoyltriphenylsilane (TBTPS), the unsubstituted thiobenzoyltriphenylsilane; yet, as it affords spin adducts whose spectra are characterized by a smaller number of lines, it may prove more useful than TBTPS itself when dealing with radicals leading to species with a large number of magnetically active nuclei interacting with the unpaired electron.

The kinetics of decomposition of oxynitroxides Me 3 CN(O . )OMR 3 , with R 3 M=Me 3 C, Bu 3 Sn, Ph 3 Ge, and Ph 3 Si, has been studied by EPR at different temperatures, and the activation parameters have been determined

The radical anions from thiobenzophenone, thiobenzoyltriphenylsilane, and 3,5-di-tert-butylthiobenzoyltriphenylsilane were detected by EPR spectroscopy when these compounds were reacted with a number of Grignard reagents, RMgBr. The radical adducts resulting from addition of R• radicals to the thiones were also detected. The formation of the radical anions indicates unambiguously the occurrence of a SET process which might be the initial stage of these reactions. In the case of tris(trimethylsilyl)ethanethial only the radical adducts were detected. The first reduction potentials of these thiones have also been measured in order to verify the feasibility of the SET process. In agreement with the EPR experiments, the calculated standard free energy changes suggest that electron transfer is possible in the first three cases and disfavored with the thioaldehyde.

The kinetics of decomposition of oxynitroxides Me 3 CN(O . )OMR 3 , with R 3 M=Me 3 C, Bu 3 Sn, Ph 3 Ge, and Ph 3 Si, has been studied by EPR at different temperatures, and the activation parameters have been determined

The direct EPR detection of thioacyl radicals has been reported only once, while thioacyl nitroxides remain an elusive species. We failed to detect the thioacyl radicals from two thioaldehydes and from phosphoryldithioformates but have obtained EPR evidence that thioacyl radicals react with 2-methyl-2-nitrosopropane to give thiocarbonyloxyaminyls rather than thioacyl nitroxides. The results of DFT calculations support this unexpected reactivity of thioacyls, while making questionable their previous EPR identification.

ESR studies carried out during the reaction of ferrocenoylsilanes with Grignard reagents at low temperature led to the detection of the radical anions of the former compounds. Cyclic voltammetric experiments indicate that the observed radical anions are likely to originate through an inner-sphere electron transfer process. Different radical species were observed upon annealing, originating from destruction of the ferrocenyl moiety. Paramagnetic species were also detected on reacting ferrocenoylsilanes with LiAlH4. Copyright © 2004 John Wiley & Sons, Ltd.

The identification of the species observed by EPR spectroscopy in the SmI(2)-promoted coupling of N-(N', N'-dialkylaminoalkyl)benzotriazoles as substituted benzyl radicals is disputed on the basis of results obtained studying the model radical derived from tribenzylamine.

The reduction of a number of phosphoryl- and thiophosphoryl formates, monothioformates and dithioformates has been studied by means of cyclic voltammetry and EPR spectroscopy. The reduction potentials of all dithioformates are close to −1 V vs. SCE, and increase for S-alkyl monothioformates and even more for O-alkyl monothioformates. The radical anions of the compounds bearing the thiocarbonyl function have been characterised by means of EPR spectroscopy, whereas those of the compounds having the carbonyl function underwent decomposition before detection. Reduction at higher potentials led in most cases to the detection of paramagnetic dianions derived from fragmentation of the initially formed radical anions.

Five of the title N-oxides 1 when reduced either chemically (phenylhydrazine, hydrazobenzene) or electrochemically (DMF–TEAP–protonating agent) were found to afford the corresponding, 5-hydroxyindoles 6. The reduction process takes place in two steps leading initially to 1,5-dihydroxyindoles 4 which undergo loss of water and are eventually converted into the products. EPR spectroscopic studies of the chemical and electrochemical reduction led to the characterization of the intermediate radical anions and neutral radicals, and a mechanism based on these results as well as on polarographic and cyclic voltammetric studies is proposed for the process.

The paramagnetic species detected by EPR spectroscopy upon electrochemical reduction of bis(2,4,7-tri-tert-butyl-phenyl)-1,3-diphosphaallene in THF solution has been unambiguously identified as the title radical, the identi-fication being supported by DFT calculations

The radical ions from 5-nitrospiro[indoline-2,3′-naphthopyran]1, 8′-nitrospiro[indoline-2,3′-naphthopyran]2, and 5,8′-dinitrospiro[indoline-2,3′-naphthopyran]3 have been investigated electrochemically and by means of electron paramagnetic resonance spectroscopy.The first reduction potentials of these compounds reflect the position of the nitro groups and vary between –1.532 V for 1 and –1.273 V for 2vs. SCE, while 3 exhibits two reduction waves at, potentials similar to those of 1 and 2, suggesting no or very little interaction between the two moieties of the molecules. The oxidation potentials are dominated by the indolinic moiety increasing in the order 2 < 1 < 3.The reduction with butoxide in DMF leads to the EPR observation of the expected radical anions of 1 and 2, while the spectrum observed with 3 shows, against expectations, reduction of the indolinic moiety. Photoreduction with Bu4NBH4 in THF affords the radical anions of 2 and 3 but not of 1, the measured hfs constants being similar to those measured in DMF without light. Addition of in situ generated triphenylgermyl radicals to 1–3 affords rather persistent germyloxy-aminoxyls which give identical spectra both under UV irradiation and in the dark.

The radical anions from thiobenzophenone, thiobenzoyltriphenylsilane, and 3,5-di-tert-butylthiobenzoyltriphenylsilane were detected by EPR spectroscopy when these compounds were reacted with a number of Grignard reagents, RMgBr. The radical adducts resulting from addition of R• radicals to the thiones were also detected. The formation of the radical anions indicates unambiguously the occurrence of a SET process which might be the initial stage of these reactions. In the case of tris(trimethylsilyl)ethanethial only the radical adducts were detected. The first reduction potentials of these thiones have also been measured in order to verify the feasibility of the SET process. In agreement with the EPR experiments, the calculated standard free energy changes suggest that electron transfer is possible in the first three cases and disfavored with the thioaldehyde.

The radical ions from bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphaallene were investigated through EPR spectroscopy, cyclic voltammetry, and pulse radiolysis. Cyclic voltammetry indicated an oxidation potential of 2.0 V vs. SCE and a reduction potential in the range –1.97 to –2.10 V vs. SCE, depending on solvent. Whilst the starting compound does not significantly absorb beyond 300 nm, the absorption spectrum of the radical cation is characterised by bands centred at ca. 320 and ca. 410 nm: according to EOM-CCSD calculations on the unsubstituted diphosphaallene the latter band should be due to a transition from the SOMO to the second LUMO, while the former might result from the overlapping of three different transitions. The EPR spectra recorded in the present study upon reduction of the title compound are far more complex than those recently published, and significant differences have been observed upon chemical or electrochemical reduction. A higher spin density on the phosphorus atoms is observed in the anion than in the cation, in agreement with the different nature of the SOMO in the two species predicted by UB3LYP calculations on the model compound diphenyl-1,3-diphosphaallene, which also predict for both ions the existence of cis and trans geometrical isomers, the latter being more stable. In both radical ions the unpaired electron is mainly localised in the PCP moiety, namely in a π-allylic type MO in the cation and in a σ MO in the anion. These pictures of the SOMO are opposite to those recently published following MP2 calculations on the unsubstituted diphosphaallene.