The ¹¹B chemical shifts of either the isolated 1 : 1 complexes or, in the absence of the formation of solid adducts, the 1 : 1 mixture of the components, have been used to investigate the donor properties of nitro- and pentafluoronitro-benzenes towards boron halides in methylene dichloride solution. The ¹⁴N chemical shifts, obtained on the same solutions, revealed no simple correlation with the donor properties although the resonance line widths reflected the acceptor properties of the boron halides. The ¹⁹F chemical shifts of complexes of pentafluoronitrobenzene are also discussed.