1. lec11 Introduction Heterocyclic compound is one wich possess a cyclic structure with at least two different kinds of atoms in the rings.The most common type, contain largely carbon atoms Nitrogen, Oxygen and Sulphur are the most common hetero atoms. Heterocyclic compounds are very widely distributed in nature, and essential to life in various ways.Most of sugar, and their derivatives including vatamine c, Vitamin B, Vitamin B6, alkaloide and antibiotic Heterocyclic compounds can be aliphatic or Aromatic in character depending upon their electronic constituents. In general, the aliphatic heterocyclic compounds are very similar to their open chain aliphatic analognes for e.g.

2. lec12 Tetrahydrofuran (1) has many properties characteristic to diethyl ether (11) In a similar way the aromatic heterocyclic have many properties resembling their aromatic carbo cyclic analogues for example pyridine (III) and benzene (IV) (III)(IV)

3. lec13 Classification of Heterocyclic compounds A – One ring 1 – Three – Membered Mono heterocycles 2 – Four – membered Mono heterocycles

4. lec14 3 – Five – membered Mono heterocycles 4 – Five membered di heterocycles

5. lec15 5 – Five – membered triheterocycles 6 – Six – membered monoheterocycles N N N | H 1 2 3 4 5 1,2,4 - triazole NN N | H 1 2 3 4 5 1,3,4 - triazole

6. lec16 7 – Six – memberd diheterocycles 8 – Six – membered triheterocycles 1 2 3 4 5 6 NN N 1,3,5 - Triazole S N O 1,4,2 - Oxathiazine 1 2 3 4 5 6 N | H N H | piperazine Morpholine N | H O N N Pyrimidine

7. lec17 B – Fused rings γ O O coumarine