Heterocyclic Compounds are those cyclic compounds in which one or more of the ring carbons are replaced by another atoms. The non- carbon atoms in such rings are referred to as hetero atoms.
The most common hetero atoms are nitrogen, oxygen and sulphur, but other atoms such as boron, phosphorus, or silicon can also members of heterogeneous rings.
A number of substances which are heterocyclic compounds according to the above definition have already been discussed in earlier chapters e.g., ethylene oxide, succinic anhydride lactones, and are easily converted into open- chain derivatives. The heterocyclic Compounds which we are about to consider here are much more stable and known. In this article we will variety our study to the most important ones which are made of five- and six- membered rings.
Nomenclature
The simple heterocyclic compounds are cat by well established common names. How ever, the more complex rings which are not within the scope of this book are named more syste- matically. The common names of some of the most important five- and six memberd hetero- cycle ring compounds are given below-
Notice that rings containing nitrogen usually end with -ole if five- membered and with -line if memberd. The hetro atoms is always numbered as 1 (isoquinoline is an exception) and in such a way as to keep the substances numbers as low as possible.
