Trinitrotoluene, in chemistry, any of several nitro substitution compounds produced by the substitution of three nitro (NO₂) groups for three hydrogen atoms in toluene (C₆H₅CH₃). Because hydrogen atoms can be replaced in both the C₆H₅ group and the CH₃ group, it becomes possible, through the different positions these three NO₂ groups may occupy relatively in the molecules, to produce 16 different trinitrotoluenes. Each of these exhibits individual characteristics, such as melting point, boiling point, specific gravity, solubility, and sensitivity to detonation. All are produced by nitration of the hydrocarbon or its products or by indirect reactions.

Symmetrical, or 2,4,6-trinitrotoluene, is commonly called TNT, the best known of the compounds. It forms pale yellow crystals of specific gravity 1.65 and with a melting point of 82° C (180° F). Its low melting point allows it to be melted and poured into artillery shells and other explosive devices. It burns in the open at 295° C (563° F), but it may explode if confined. In the absence of a detonator, it is a rather stable material, does not attack metals, does not absorb moisture, and is practically insoluble in water. TNT dissolves in benzene and in acetone and, like all nitro compounds, reacts readily with substances that surrender electrons, that is, with chemical reducing agents. High-velocity detonators, such as mercury fulminate and nitramine, induce its violent and explosive decomposition. TNT can be absorbed through the skin, causing headache, anemia, and skin irritation. See Explosives.