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The reaction of sodium isopropoxide with 2,4,6-trinitrotoluene (TNT) and TNT-d3 (deuterated methyl group) in isopropanol has been investigated using stopped-flow techniques. Two absorbing species, identified as a σ-complex and the TNT anion (TNT−) are formed in this reaction. The formation of TNT− involves a rate determining proton transfer as shown by the observation of an isotope effect[Formula: see text] A spectrum of the σ-complex was calculated from initial rate data and was observed experimentally at low temperatures (λmax = 435, 495 nm). The effects of added salts on rates and equilibria of σ-complex and TNT− formation have been determined.In this study the possible involvement of free alkoxide ions and ion-pairs in the reactions has been evaluated. The free alkoxide ion is the more reactive species in deuteron transfer whilst in σ-complex formation the free ions and ion-pairs have comparable reactivity. A rationale of this behavior is presented.The kinetic parameters are, for deuteron transfer: kiD = 850 ± 100 M−1s−1 at 30 °C, ΔH≠ = 14.9 ± 1.1 kcal mol−1, ΔS≠ = 5.1 ± 2.9 cal deg−1 mol−1; for σ-complex formation: k′ = 1870 ± 150 M−1 s−1 at 30 °C, ΔHσ≠ = 10.2 ± 0.3 kcal mol−1, ΔSσ≠ = −9.8 ± 1.1 cal deg−1 mol−1.