N-π Electron donor–acceptor complexes. III. Aliphatic amines with dicyanobenzenes. Electric and steric effects of the N-substituents on complex formation

Abstract

The interaction of several aliphatic amines as n-donors with 1,2-, 1,3-, and 1,4-dicyanobenzenes as π acceptors in n-hexane has been studied. The spectroscopic behaviour of the mixtures leads us to propose that Electron Donor – Acceptor (EDA) complexes are formed. Correlations of the experimental data with the amine structure were performed for the amine–1,4-dicyanobenzene complexes. By means of free energy related substituents and regression analysis, the electronic and steric effects of three N-substituents were quantitatively separated. Thus, with K representing the stability constants of the complexes, the values of log K are correlated with Taft's polar substituent constants, σ*, and Hancock's corrected steric substituent constants, [Formula: see text] The results allowed the proposal of a probable structure of the complex, at least with respect to the donor orientation.