A 13C NMR chemical shift prediction and spectral assessment program was written in Turbo Prolog. Based on the large data compendium of Ewing it allows the rapid assessment of the spectral–structural relationship for substituted benzene rings.

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Generation of a-fluorobenzyl radicals during thermal decomposition of diazodiphenylmethanes or benzoyl peroxide in benzyl fluoride as solvent or in the decomposition of t-butyl a-fluorophenylperacetate gives rise inter alia to mem and (*)-difluorobibenzyl. However, CIDNP observed in l9F-spectra does not appear to match the pattern of signals of these products. The inference, in a preliminary report, that the dimerisation takes place in two stages, a head-to-tail co-ordination giving a semibenzene followed by rearrangement, is shown to be incorrect. Examination of the effect on the pattern of lgF-polarisation of introducing deuterium into the phenyl ring and into the side-chain of a-fluorobenzyl radicals indicates that the predominant mode of dimerisation must be head-to-head giving directly meso-and (*) -1,2-difluoro-l,2-diphenylethanes. This conclusion is confirmed by computer simulation of the polarised spectrum.

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