Theoretical Studies to the Electrophilic Attack. VIII. The Protonated Pyrrole The potential surface of protonated pyrrole was analysed for minima and saddle points of first and higher order by special numerical methods. The calculations were carried out on the basis of semiempirical methods tested in the past on related cationic systems. The relative energies of face protonated pyrrole, the σ‐complexes and H‐bridged structures were compared with recent results on the benzene‐H+ system to interprete the H‐shifts in the cation and the intermediates in the proton exchange reaction. Theoretical suggestions for solvatation effects are considered in the discussion. One of the most striking results is the high barrier for the H‐shift from the N‐protonated form to the α‐position.

Theoretical Studies on the Electrophilic Attack. IX. Intramolecular H‐Shifts in the ortho‐Disubstituted Aromatic Compounds o‐Xylene and 1, 2‐Difluorobenzene A potential energy characterization of the proton shifts in the above cited 1, 2‐disubstituted aromatic compounds and their dependence on solvent influence are studied by means of theoretical methods. The results complete in many points our knowledge of experimental data in solution estimated from n. m. r. spectroscopic investigations.