Nomenclature of Heterocycles
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
Introduction to Heterocycles
Heterocycles, the diverse class of organic compounds containing at least one ring structure with atoms of at least two different elements, play a crucial role in various fields, from medicinal chemistry to materials science. Understanding the nomenclature of heterocycles is fundamental for anyone delving into the realm of organic chemistry.
Nomenclature of Heterocycles
IUPAC Rules for Naming Heterocycles
The International Union of Pure and Applied Chemistry (IUPAC) provides standardized rules for naming heterocycles. These rules establish a systematic approach to nomenclature, simplifying the communication of complex structures.
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,..
FAQs (Frequently Asked Questions)
- What is the significance of heterocycles in medicinal chemistry?
- Heterocycles often form the core structure of many pharmaceutical compounds, influencing their biological activity.
- How does IUPAC contribute to the standardization of heterocyclic nomenclature?
- The International Union of Pure and Applied Chemistry establishes rules that provide a systematic approach to naming heterocycles, ensuring uniformity in communication.
- Why are five-membered heterocyclic rings commonly encountered in organic chemistry?
- The stability and prevalence of five-membered rings are attributed to their favorable bond angles and strain-free structures.
- Can you provide examples of famous heterocyclic compounds with significant scientific contributions?
- Yes, compounds like caffeine, DNA bases, and vitamin B12 are notable examples of heterocyclic compounds with profound scientific importance.
- How can students overcome challenges in memorizing heterocyclic nomenclature?
- Developing mnemonic devices, practicing consistently, and understanding the underlying principles can aid in memorization.
Also, Visit:
B. Pharma Notes | B. Pharma Notes | Study material Bachelor of Pharmacy pdf