Chemically induced dynamic polarisation of¹⁹F nuclei in the dimerisation of α-fluorobenzyl radicals

Abstract

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.

The barrier to internal rotation in benzyl fluoride investigated using the N.M.R. spectra of samples dissolved in liquid crystalline solvents

“…A sample of benzyl fluoride-or,or-d2 was synthesized by the method of Bethell et al [14]. Ethyl benzoate was reduced with LiA1D a to the alcohol, which was then reacted with PBr 3 and the benzyl bromide-~,~t-d2 was refluxed for a week at room temperature in a suspension of KF in 18-crown-6 ether and acetonitrile.…”

4,5,6-Tri-O-benzoyl-2,3-di-S-ethyl-2,3-dithio-D-allose diethyl dithioacetal

“…in the presence of an acid catalyst a tetrathio product (I) is obtained which, initially (Brigl & Schinle, 1932), was described as 3,5,6-tri-O-benzoyl-2,4-di-S-ethyl-2,4dithio-o-glucose diethyl dithioacetal. A reinvestigation, however, (Bethell & Ferrier, 1972a,b, 1973 led to the conclusion that the compound carried the ethylthio groups at C(1), C(1), C(2) and C(3) (2) 3373 (5) -123 (6) 8170 (2) S(3) 5912 (5) 1540 (6) 6690 (2) 0(4) 7846 (9) 1060 (10) 8212 (4)…”

Chemistry of novel compounds with multifunctional carbon structure. Part 4. Steric and electronic influences on the diastereoisomeric chemical shift differences in 19F n.m.r. spectra by introduction of fluorine, phenyl, and heteroatom groups into acetates

“…In a preliminary experiment,* however, an unfortunate problem of racemization at the benzylic position seemed to arise when attempts were made to obtain the optically active form of (12). Further investigations, including preparation of optically active forms of (8)- (11) and elucidation of the possible heteroatom effect, are under way.…”