SEARCH Articles Figures Tables At nitrogen Eight-Membered Ring Preserved Substitution at Nitrogen, Sulfur, and Carbon Electrophilic substitution at nitrogen Nitrogen Substitution Nitrogen, substitutional Nucleophilic Substitution at the Nitrogen, Phosphorus, and Sulfur Centers Substitution at Substitution at the Nitrogen Atom of Nitroso- and Nitro-Groups Substitutions at pyrrole nitrogen Tautomer Ratio in the Imine-Enamine System Substitution at Nitrogen