Studies on complexes. Part XI. Acceptor properties of some perhalogenobenzenes

Abstract

Suitability of the formula C_wN_xO_yF for describing electron acceptor molecules is discussed. New absorptions, many of them associated with colours, of some perhalogenobenzenes with NN-dimethylaniline, NNN′N′-tetramethylphenylenediamine, and tetrakis(dimethylamino)ethylene are ascribed to charge-transfer transitions. In cyclohexane weak 1:1 complexes are formed and ΔG, ΔH, and ΔS values are determined spectrophotometrically. The hexachlorobenzene complexes are stronger than the hexafluorobenzene complexes and their spectra are displaced further into the visible region, although from the positions of the absorptions both acceptors are weaker than nitrobenzene. Chloropentafluorobenzene interactions are anomalous in the series and are discussed in terms of the low symmetry of the acceptor molecule and a preferred orientation in the complex. Close to zero equilibrium constants for the tetra-aminoethylene systems are ascribed to the bulk of this donor.