Heterocyclics are cyclic compounds

Heterocyclics are cyclic compounds containing one or more heteroatoms (nitrogen, sulfur, or oxygen) in addition to carbon atoms. The dioxins already discussed as well as other
compounds shown in Figure 20.11 fall into this category. In general, heterocyclic compounds are more difficult to degrade than analogous aromatics that contain only carbon. This is probably due to the higher electronegativity of the nitrogen and oxygen atoms compared with the carbon atom, leading to deactivation of the molecule toward electrophilic substitution. Heterocyclic compounds with five-membered