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The reductive electron transfer (ET) induced on a series of RCCl3 derivatives by iron(II) chloride has been studied. The main reaction products are the homocoupling dimer, RCCl2–CCl2R, and the H/Cl substitution derivative, RCHCl2, and the majority of the compounds examined exhibit a highly selective tendency to form just one of these products. As a general rule, the RCHCl2 compound is the main product when the R group contains substituents which make further reduction of the radical to the carbanion easier and behave as ligands towards the iron(II) ion. In the other cases, the dimer RCCl2–CCl2R is the main product. A few exceptions are found, and these are discussed in view of the possible effects of the R moiety on the different possible routes for the reaction products. The presence of unsaturated derivatives, RCClCClR (E/Z mixture), was observed in the case of the reactions where the homocoupling product was also obtained and is ascribed, on the basis of experimental evidence, to a dehalogenation mechanism of the dimer RCCl2–CCl2R assisted by the iron(II) ion.

Reduction of trichloromethyl derivatives RCCl3[1, R = Ph; 2, R = PhC(O);3, R = EtOC(O)] with iron(II) chloride in acetonitrile, has been studied in order to examine the mechanism of the electron transfer (ET) process and the reactions of the radicals formed. Substrates 1–3 afforded different product compositions and the cause was identified as differences in the reactivity of radicals which is substantially of two types: reductive coupling and proton abstraction after further reduction to a carbanion coordinated to the metal ion. Compound 1 gave only coupling products, compound 2 only hydrogenated products and compound 3 a mixture of coupling and hydrogenated products depending on experimental conditions. Proton abstraction by the carbanion was found to occur from water molecules, which should be present in the coordination shell of the metal ion, and not from the solvent. The different behaviour of compounds 1–3 is attributed to the presence of substituents which are able to stabilize the radical and carbanionic intermediates. Rate constants at different temperatures were measured and the activation parameters calculated. The three substrates differ only slightly in reaction rates, in the order 1 > 2 > 3. Activation enthalpies are very close to each other and this agrees with the almost equal values of C–Cl bond dissociation energies of compounds 1–3, empirically determined. Large, negative entropies of activation were found, suggesting that an ordered activation complex should be formed in order that electron transfer from the metal ion to the organic halide can take place.

The 17O chemical shifts and band widths for tert-butyl peresters of ortho-substituted benzoic acids have been measured in benzene solution. Two signals are observed, of different line-width, and that at higher field is broader. The two signals shift to lower field with an increase in the number and size of ortho substituents (methyl and tert-butyl groups were chosen), and the signal at lower field is the one more significantly affected. Correlations with a fair degree of linearity are found for each set of chemical shifts with the twist angle of the carbonyl group from the phenyl plane. Twist angles were calculated from molecular mechanics. From the screening constant estimated theoretically at a semi-empirical level with the Karplus–Pople formula and from line-width arguments based on quadrupole relaxation, it is possible to advance the reasonable conclusion that the signal at lower field of these molecules represents two oxygen nuclei [those of the C(O)–O group] and the other the remaining peroxidic oxygen. For the 2,4,6-tri-But derivative which is solid at room temperature and can be obtained in a suitable crystal form, the crystal and molecular structure has been determined by X-ray diffraction. The structure is built up of one crystallographically independent molecule, affected by statistical disorder due to two alternative orientations of all the tert-butyl groups bonded to the ring. The peroxycarboxyl group is planar and nearly perpendicular (80.8°) to the benzene ring plane.