D. Lefort

Relations between chemical structure and gas chromatography I. Branched esters

The authors have investigated the chromatographic behaviour of esters having the general formula Open image in new window A1, A2, B1, B2, B3 being alkyl substituents. By means of the differences in equivalent chain lengths on two stationary phases, one polar, the other non-polar, it is possible to determine the “apparent polarity” of the ester function. The results show that this polarity is related to the steric hindrance of the function.

Peracids and free radicals: A theoretical and experimental approach

Organic peracids behave as a source of alkyl radicals and serve as a good model for studying their chemistry. The OH transfer by alkyl radicals and the stereoelectronic control of the reaction were investigated in detail. Inter- and the intramolecular hydrogen shifts by alkyl radicals were also studied. These results were used in order to undertake selective hydroxylation of hydrocarbons. Finally we turned our attention to the reactivity of electrophilic radicals towards peracids.

Decomposition of peroxydecanoic acid using BCHPC [di(4-tert-butylcyclohexyl) peroxydicarbonate] under argon atmosphere

Using BCHPC as a source of alkoxycarbonyloxyl radical at moderate temperature in benzene or cyclohexane and in the absence of O2(under argon), the peroxydecanoic acid RCO3H is transformed into nonan-1-ol ROH in good yield. A mechanism, implying the acylperoxyl radical RCO3˙ as an intermediate, is proposed.

Decomposition de l'acide peroxydodecanoique dans CCl4 : role du solvant

Abstract The decomposition of peroxydodecanoic and in refluxing CCl4 proceeds by a complex process involving ionic and radical reactions. In the latter, this study has confirmed the important role, shown previously,1 of the character(nucleophilic or electrophilic) of the radical on the regioselectivity of the attack on the peracid.

Caractere polaire du radical phenyl-2 cyclopropyle: regioselectivite de la reactions la fonction peroxyacide

Abstract A study of the reactivity of the 2-phenylcyclopropyl radicals obtained by thermal decomposition of 2-phenylcyclopropane carbonxylic peracids in benzene or cyclohexane solution is presented. It was found that these reactions led to the formation of phenylcyclopropane and its corresponding acid and not to the formation of 2-phenylcyclopropanol. Its appeared that the stereochemistry of the starting peracid did not influence the course of these reactions. These results led us to conclude that the 2-phenylcyclopropyl radical was very weakly nucleophilic towards the OO peracid bond and that it reacted essentially by H-abstraction. Its low nucleophilicity which is similar to that of the phenyl radical but most likely lower than that of the bicyclo [2.2.1] 1-heptyl radical is probably due to its pyramidal structure.

On the Role of the Orbital Interaction Concept in the Interpretation of Organic Free Radical Structures and Reactivities

Molecular Orbital (MO) theory is probably the most powerful theoretical tool available to organic chemists. Quite early it became clear that MO theory and its related concept of orbital interaction can provide a pictorial and attractive description of organic molecules and represent a particularly suitable basis for building up a fruitful theory of structure and reactivity.

Interpretation of the reactivity of benzyl free radical towards peroxyacids in terms of orbital interactions. Competition between energy gap control and overlap control

The factors which control the reactivity of alkyl free radicals R˙ in reaction (i) are studied. The reactivity [graphic omitted] R′→ R – OH + R′CO˙2(i), of R˙ in (i) depends on the key orbital interaction between the SOMO of the radical and the LUMO of the peroxyacid. This interaction involves two contributions: (i) the energy gap SOMO–LUMO and (ii) the overlap SOMO–LUMO. In reaction (i) the main factor is overlap control which depends on spin delocalisation in the radical R˙. This proves that reaction (i) does not involve electron transfer. The energy gap control, which depends on the nucleophilic character of R˙, is only observed when the first factor is constant along a series of R˙.