Enthalpies of solution of two Meisenheimer sigma-adducts of sym.-trinitrobenzene and tetrabutylammonium bromide were measured in pure dimethylsulfoxide (DMSO) at 298.15 K using a precise isoperibol calorimeter. The enthalpic coefficients of solute-solute pair-interactions and standard enthalpies of the electrolyte solution were evaluated. It has been found that the interaction between tetrabutylammonium cation and 1,1-dimethoxy-2,4,6-trinitrocyclohexa-2,5-dienide anion is enthalpically attractive, but the interaction of tetrabutylammonium cation with bromide-ion and especially with 6,8,10-trinitro-1,4-dioxaspiro[4.5]-deca-6,9-dienide anion is enthalpically repulsive. (C) 2003 Elsevier B.V. All rights reserved.