Two kinds of nitrating reagents, a nitronium cation [Formula: see text] and a nitro radical (· NO 2), were used in the gaseous phase toluene mononitration reaction. The closed shell calculation for electrophilic substitution and open shell calculation for radical substitution were both performed in solventless, H 2 O -solvated, and CH 3 OH -solvated molecular reaction systems. In the series of electrophilic toluene nitration reactions, both ortho-nitro toluene (o-MNT) and para-nitro toluene (p-MNT) are more abundant products than meta-nitro toluene (m-MNT), no matter what solvent is used in the reaction system. The reaction energy barrier for obtaining each kind of mononitro toluene follows a stepwise decreasing trend when the reaction is carried out in the solventless, H 2 O -solvated, and CH 3 OH -solvated systems. In all radical toluene nitration reactions, solventless or solvated, m-MNT is the most abundant product. The energy barrier data also show that the nitration reaction is more feasible in a solvated than in a solventless system. H 2 O has a more obvious solvent effect than CH 3 OH in the · NO 2 radical substitution reaction, and the H 2 O -solvated system provides a lower activation energy reaction path.