Electron spin resonance studies. Part XXXII. Information from hyperfine splittings for aliphatic radicals about shape and conformation

Abstract

A previous study of the relationship between the hyperfine splitting parameters of an aliphatic radical and the geometry at its tervalent carbon atom has been extended to a wider range of radicals. In particular, the significance of a(¹³C) is discussed, data for some simple ketyls ·CR¹R²·O^– are reported and interpreted, and it is suggested that useful information is available from the raio a(Me) :a(H) both for radicals ·CHMe·X and for the pairs of radicals ·CMeXY and ·CHXY. It is noted that, in radicals of the type ·CHY·CH₂X (X = an electronegative substituent, Y = OH or OR), a(CH₂) is unusually low; it is argued that this is a manifestation of an interaction which is associated with an eclipsed conformation of the C–X bond and the half-filled orbital and also with less deformation from coplanarity at the tervalent carbon atom than in the absence of X. Finally, INDO calculations for some small cyclic radicals support the conclusion from the experimental data that the species are not coplanar at the tervalent carbon atom.