Density functional study of ortho-substituted phenyl cations in polar medium and in the gas phase

► Ortho-substituted phenyl cations form rings in the gas phase. ► The corresponding transition states are reactants-like. ► The singlet state of 2-nitrophenyl cation cannot exist in the gas phase. ► The S → T transition in 2-nitrophenyl cation is proceeding due to the SOC effect.