Nomenclature of Diverse Heterocycles

Abstract This chapter is entirely devoted on the nomenclature of various monocyclic, bicyclic, tricyclic, and polycyclic, including ortho-fused, ortho-peri-fused, bridged, and spiro, heterocycles with one or more similar or dissimilar heteroatoms present in the cyclic system. In heterocyclic chemistry every heterocyclic system has a special name, while individual compounds are named also by a trivial name based on their origin of occurrence or on their special properties. Hantzsch and Widman introduced methods for naming the five- and six-membered heterocycles, which later on extended to saturated, unsaturated, and other ring sizes of heterocyclic compounds. In this system an appropriate prefix is used for heteroatoms and their ring size. The stem ol (ole) has been used in the case of five-membered heterocycles, while the in (ine) stem is used for six-membered heterocycles. Difficulties arose in naming some ortho or ortho-peri-fused, bridged, and spiro heterocyclic ring systems by the Hantsch-Widman nomenclature, and a set of rules were framed for systematic names of such heterocycles by the International Union of Pure and Applied Chemistry, which is used most frequently worldwide. Replacement nomenclature, also known as “a” nomenclature, has been used to name the heterocyclic compounds in which prefixes end with “a” and the position and prefix for each heteroatom precede the name of corresponding hydrocarbons.