Ring Versus Nitrogen Protonation of Anilines

Ionization of mixtures of halogenobenzenes and ammonia under chemical ionization conditions affords isomeric (N or C4) protonated anilines. The N-protonated species are dominantly produced by ionmolecule reactions of mass-selected ionized halogenobenzenes with ammonia or in electrospray conditions. Quantum chemical calculations confirm that the N-protonation in aniline is marginally favored, by about 4 kJ mol-1, over the C4-protonation.