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Heterocyclic Chemistry Heterocyclic Chemistry Heterocyclic Chemistry Nomenclature of Heterocyclic compounds Heterocyclic Chemistry Nomenclature of heterocyclic compounds There are three systems for naming heterocylic compounds: The common nomenclature: which convey little or no structural information but it still widely used. The Hantzsch-Widman (IUPAC or Systematic) method which in contrast is designed so that one may deduce from it the structure of the compound. The replacement method Heterocyclic Chemistry I-Common Nomenclature 1) Each compound is given the corresponding trivial name (which should be memorized, see the following slides). This usually originates from the compounds occurrence, its first preparation or its special properties. 2) If there is more than one hetroatom of the same type numbering starts at the saturated one, e.g. imidazole. Common Nomenclature Heterocyclic Chemistry 3) If there is more than one type of the heteroatoms, the ring is numbered starting at the hetroatom of the higher priority (OSN) and it continues in the direction to give the other hetroatoms the lower numbers as possible. Heterocyclic Chemistry Common Nomenclature 4) If substituents are present, their position should be identified by the number of the atoms bearing them and then they should be listed in alphabetical order. Common Nomenclature Heterocyclic Chemistry 5) The words dihydro, or trihydro, or tetrahydro are used if two or three or four atoms are saturated. These words are preceded by numbers indicate the position of saturated atoms as low as possible and followed by the corresponding fully unsaturated trivial name. Heterocyclic Chemistry Trivial names 1) 5-membered heterocycles with one or two heteroatoms 2) 6-membered heterocycles with one or two heteroatoms Heterocyclic Chemistry Trivial Names 3) Fused heterocycles Heterocyclic Chemistry Trivial Names Heterocyclic Chemistry Trivial Names 4) Saturated heterocycles Exercise : Give the com