Heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring (s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties and applications of these heterocycles. Examples of heterocyclic compounds include all the nucleic acids, the majority of drugs, most biomass (cellulose and related materials), and many natural and synthetic dyes. Heterocyclic compounds can be usefully classified based on their electronic structure. The saturated heterocycles behave like the acyclic derivatives. Thus, piperidine and tetrahydrofuran are conventional amines and ethers, with modified steric profiles. Therefore, the study of heterocyclic chemistry focuses especially on unsaturated derivatives, and the preponderance of work and applications involves unstrained 5- and 6-membered rings. Included are pyridine, thiophene, pyrrole, and furan.