First Semester

•Heterocycles form the largest class of organic compounds. In fact, many natural products and most drugs contain heterocyclic rings. The colours of flowers and plants, antibiotics known to all as penicillins, compounds that transport the oxygen we breathe to our vital organs, and the components of DNA responsible for the genetic code are all heterocyclic compounds. From an organic chemist’s viewpoint, heteroatoms are atoms other than carbon or hydrogen that may be present in organic compounds.

•The most common heteroatoms are oxygen, nitrogen, and sulfur. In heterocyclic compounds, one or more of these heteroatoms replaces carbon in a ring.