Electron-donor–electron-acceptor association constants of pyrene with 2,4,6-trinitrotoluene in solution determined by 1H-nuclear magnetic resonance from non-linear Scatchard plots

Abstract

The chemical shifts of the ring and methyl protons of 2, 4, 6-trinitrotoluene have been measured as a function of the concentration of added pyrene in solutions in carbon tetrachloride at 33.5 °C. Simple analysis at the 95 % confidence level yields association constants K= 8.42 ± 0.1 and 7.92 ± 0.1 kg mol^–1 from these two probes, respectively. Allowance for ‘additional unspecific shielding’ increases these values to K= 9.10 ± 0.05 and 8.84 ± 0.06 kg mol^–1. Alternatively, analysis based on a double equilibrium forming complexes with stoichiometry DA and D₂A results in association constants K₁= 8.7 ± 0.2 and 8.4 ± 0.3 kg mol^–1, and K₂= 0.23 ± 0.05 and 0.31 ± 0.07 kg mol^–1 from H_Ar and H_Me, respectively. Thus, whilst the model of a simple 1:1 association is untenable, the data do not provide a clear choice between the second and third models in this particular system.