Nomenclature of Heterocycles

Heterocyclic chemistry

Session Objectives

By the end of this session, students will be able to:

• Discuss Nomenclature of heterocycles

• Classify heterocyclic structures of 3, 4, 5 and 6 membered rings, fused systems with examples

Nomenclature of heterocycles

Systematic method of nomenclature:

• The prefix in the name of monocyclic compound indicates the nature of heteroatoms present

• e.g., oxygen-oxa,

              Sulphur-thia,

              nitrogen-aza,

              silicon-sila,

              phosphorus-phospha

• When two or more of the same heteroatoms are present, prefixes di, tri, etc., are used- e.g., dioxa, triaza

• If the heteroatoms are different, their Order of naming will be- O,S,N,P,Si,…-

• e.g., thiaza (S then N)

• State of hydrogenation is indicated in the suffix (as per table)

• Or prefix like dihydro, tetrahydro, etc., or by prefixing the name of unsaturated compound with symbol H preceded by a number indicating the position of saturation

• In a monocyclic compound containing only one heteroatom, numbering starts at this atom to give the substituent lowest possible number

• If heteroatoms are different, then numbering starts with as- O, S, N, P, S, Si,..

• Systematic method of nomenclature

No. of members in the ring	Rings containing nitrogen		Rings containing no nitrogen
	Unsaturation	Saturation	Unsaturation	Saturation
3	-irine	-iridine	-iren	-iran
4	-ete	-etidine	-et	-etan
5	-ole	-olidine	-ole	-olan
6	-ine	B	-in	-ane
7	-epine	B	-epin	-epan
8	-ocine	B	-ocin	-ocan
9	-onine	B	-onin	-onan
10	-ecine	B	-ecin	-ecan

• B- expressed by prefixing ‘perhydro’ to the name of the corresponding unsaturated compound

Heterocyclic systems- 3&4 membered

Heterocyclic systems- 5 membered

Heterocyclic systems- 6 membered

Fused heterocyclic systems

Summary

• The prefix in the name of monocyclic compound indicates the nature of heteroatoms present

• State of hydrogenation is indicated in the suffix (as per table)

• If the heteroatoms are different, then numbering starts with high group in periodic table as- O, S, N, P, S, Si,..