Equilibrium constants of complex formation between the strong electron acceptor 1,3,5-trinitro-benzene (TNB) and basic donors (n-butyl-amine and piperidine) were determined by positron annihilation lifetime technique. The reaction rate costants of the complexes with o-Ps were calculated too. The results were compared with our earlier investigation on TNB in methanolic solutions of NaOH Ill. All the complexes formed were so called Meisenheimer complexes 121. The stability of the complexes and

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... ir reactivity towards o-Ps can be accounted for by the differences in their structure, in the size of the donor molecules and in the charge distribution on the complexes.