We performed second order perturbation theory calculations of gas phase proton affinities for o, m, p-nitroaniline at all positions and attempted correlations of the thermodynamic stability of the products with several reactivity indices: inductive effects from resonance, partial charges, and frontier orbital related indices such as local nucleophilic and electron-donating powers, global hardness of the products, and the substituent push-pull effect. All protonation reactions at ring positions are predicted to be exothermic. Resonance and charge analysis give inconsistent correlations with proton affinities, while the condensed nucleophilic Fukui function, electron-donating power, global hardness, and push-pull effect show promising trends.