1:1, 2:1, and Apparent association constants for a series of electron donor–acceptor complexes involving 1,3,5-trinitrobenzene and tetrafluoro-p-benzoquinone (fluoranil)

Abstract

On the hypothesis that in certain solutions termolecular as well as bimolecular complexes are formed between π-donor and π*-acceptor molecules, the apparent, 1 : 1, and 2 : 1 association constants have been estimated for the series of donors: benzene, toluene, p-xylene, mesitylene, durene, pentamethylbenzene, and hexamethylbenzene with 1,3,5-trinitrobenzene in cyclohexane, and of the same series of donors with fluoranil in carbon tetrachloride. The results indicate that within these two groups of complexes of a set of structurally related donors and a common acceptor the apparent association constant is directly proportional to the 1 : 1 association constant (and also to the corresponding 2 : 1 association constant). This observation suggests that a number of published values of apparent association constants for such series of complexes are of use in making comparisons within the particular group, although the evidence given in the present paper suggests that such comparisons between groups might be misleading. The same comments apply to quantities which are dependent in their experimental estimation on an implicit or explicit knowledge of the concentration of the complex in solution (e.g. the molar absorption coefficient of the complex).