Reactivity of acetonyl anion with nitroaromatics: An atmospheric pressure chemical ionization study

Nucleophilic attack by the acetonyl anion (CH₃COCH ₂^-) on highly electron-deficient nitroaromatics such as trinitrotoluene (TNT) results in the carbon-bonded anionic σ-complexes (Meisenheimer complexes). The complexes are generated at atmospheric pressure with relatively low internal energy and do not dissociate under atmospheric pressure chemical ionization conditions, but can be dissociated upon collisional activation to produce characteristic nitrobenzyl-substituted acetonyl anions via elimination of HNO₂. Further fragmentation produces deprotonated nitrotoluene anions through the loss of CH₂CO, while loss of CH ₂COCH₃ and CH₃COCH₃ yields nitroaromatic molecular anions and their H-loss counterparts. Hydrogen/deuterium (H/D) scrambling is observed in the fragmentation products of the [TNT·CD₃COCD₂]^- complex to extents which vary for different fragmentation pathways. Selective Meisenheimer complex formation, together with its distinctive fragmentation pattern, supplies a highly discriminatory method for detection of TNT and related compounds.