Heterocyclic compounds nomenclature POC III

students able to get knowledge on heterocyclic compounds nomenclature

1. UNIT III
HETEROCYCLIC
COMPOUNDS
Presented by
P.SOWMIYA
Assistant Professor
Dept. of Pharmaceutical Chemistry
SVCP

2. INTRODUCTION
Heterocycliccompoundsarethosecycliccompoundsin
whichoneormoreoftheringcarbonarereplacedby
anotheratom.
Thenon-carbonatomsinsuchringsarereferredtoas
Heteroatoms.
Mostcommonheteroatomsare
➢Nitrogen
➢Oxygen
➢Sulphur
➢Boron
➢Phosphorous
➢Silicon

3. IMPORTANCE OF HETEROCYCLIC
COMPOUNDS
Heterocyclic compounds are very widely distributed in nature and
are particularly important because of wide variety of physiological
activities.
Important compounds containing heterocyclic rings are
❖Vitamins
❖Alkaloids
❖Chlorophyll
❖Amino acids
❖Dyes
❖Drugs
❖Enzymes
❖DNA
❖Genetic material

4. NOMENCLATURE
There are Two systems for naming Heterocyclic compounds
NOMENCLATURE
I. TRIVIAL/ COMMON
NAMES
II. SYSTEMATIC/
IUPAC NAMES
A) Hantzsch
Widman system
B) Replacement
method

5. I. Trivial or common names
They convey little or no structural information but it still widely
used.
Eg:O
Ethylene oxide NH
Pyrrole O
Furan S
Thiophene NH
N
Imidazole N
Pyridine NH
Indole

6. II. Systematic/ IUPAC NAMES
A) HANTZSCH-WIDMAN METHOD
AccordingtoIUPACSystemofnomenclature
(InternationalUnionofPureandAppliedChemistry),the
namesofheterocycliccompoundsaremadeupofthree
parts:
i.Stemindicatesringsize
ii.PrefixdescribesHeteroatom
iii.Suffixdenotesthedegreeofunsaturation

7. Prefixes for hetero atoms
Hetero atom Valence Prefix
O 2 Oxa
N 3 Aza
S 2 Thia
Se 2 Selena
Te 2 Tellura
P 3 Phospha
As 3 Arsa
Si 4 Sila
Ge 4 Germa

8. Stems and Suffixes for naming
Heterocyclic compounds
Ring sizeStem Unsaturated
compound
Saturated
compound
With NWithout NWith NWithout N
3 -ir- -irine -irene -iridine-irane
4 -et- -ete -ete -etidine-etane
5 -ol- -ole -ole -olidine-olane
6 -in- -ine -in - -ane
7 -ep- -epine -epin - -epane
8 -oc- -ocine - -ocin -ocane

9. Rules for Systematic nomenclature
1) IUPAC Name = Prefix + stem + suffix
Combine the prefix and suffix together and drop the first
vowel if two vowels came together.
Eg:
Oxa+ irane
OxiraneO

10. NH NH N

11. NH
Aza+ etidine
Azetidine
Aza+ ole
Azole
Aza+ ine
Azine

12. O O NH O O

13. O O NH O O Oxa+ ine
oxine
Oxa+ ane
oxane
Oxa+ epane
oxepane
Aza+ epine
Azepine
Oxa+ epin
oxepin

14. 2)Inthenumberingofheterocyclicrings,theheteroatomis
alwaysgivennumber1
3)Whentwoormoreheteroatomsofsametypearepresent
inaring,prefixeslikedi,tri,tetraetc.,areusedbeforethe
heteroatomname.NH
1 2
3
5
4
Pyrrole 5
O
1
4
2
O
3
1,3- dioxolane NH
NH
NH
1,2,3- triazole
1
2
3 4
5

15. 4)Whentwoormoredifferentheteroatomsarepresentinasame
ring,prefixesofheteroatomsarecombinedintheorderofpriority.
(order–O,S,N,P,Si)
5)Numberingisdonearoundtheringinthatdirectionwhichgivesthe
lowestnumbertothesubstituents.O
1 2
3
5
4
NH
2
6
3-amino-1-oxazole O
1 2
N
3
5
4
Oxazole

16. 6)Thestateofhydrogenationisindictedbyprefixlike
dihydro,tetrahydroorbyprefixingHprecededbyanumber
indicatingthepositionofsaturation.
7)Incaseofbenzofusedheterocycliccompounds,prefixthe
wordbenzofollowedbypositionoffusioninsquarebrackets
andnameofheterocyclicring.O
b
c
d
e
a
Benzo[b]furan S
a
b
c
d
e
Benzo[c]thiophene NH
1 2
3
5
4
1-H Azole/
1-H Pyrrole O
Tetrahydrofuran

17. 8)Numberingoffusedpolycyclicheterocyclic
compoundsfollowsthenumberingsystemof
carbocyclicsystem.N
Quinoline
1
2
3
45
6
7
89
10

18. B) REPLACEMENT NOMENCLATURE
Inthismethod,theheterocycle'snameiscomposedof
correspondingcarbocycle’snameandprefixfortheheteroatom
isintroduced.S
CyclohexaneThiocyclohexane N
Naphthalene 1-Azanaphthalene

19. CLASSIFICATION OF
HETEROCYCLIC COMPOUNDS
Depending on
I.Size of heterocyclic ring
II.Number of rings present
III.Aromaticity