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Nomenclature of
Heterocyclic Compounds

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I
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II
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The Replacement Nomenclature

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Hantzsch-Widman Nomenclature

n = 1,2,3, ……

The Hantzsch-Widman nomenclature is based on
the type (Z) of the heteroatom; the ring size (n) and
nature of the ring, whether it is saturated or
unsaturated
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Type of the heteroatom
The type of heteroatom is indicated by a
prefix as shown below for common
hetreroatoms:
Hetreroatom
O
N
S
P
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Ring size (n)
The ring size is indicated by a suffix according to
Table I below
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Table I: Stems to indicate the ring size of
heterocycles
Ring size
3
4
5
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Table II: Stems to indicate the ring size and degree of
unsaturation of heterocycles
Ring size Saturated

Unsaturated Saturated (With Nitrogen)

3
4
5
6
7
8
9
10

-irine
-ete
-ole
-ine
-epine
-ocine
-onine
-ecine

-irane
-etane
-olane
-inane
-epane
-ocane
-onane
-ecane

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The letter “a” in the prefix is omitted
where necessary
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It is important to recognize that the saturated
suffix applies only to completely saturated ring
systems, and the unsaturated suffix applies to
rings incorporating the maximum number of noncumulated double bonds
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Solomon Derese

SCH 402

19

Systems having a lesser degree of
unsaturation require an appropriate prefix,
such as "dihydro"or "tetrahydro"
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Solomon Derese

Thia+olane= Thiolane
SCH 402

Aza+iridine= Aziridine

Aza+etidine=Azetidine

Aza+olidine= Azolidine
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Azine

Azinane

Pyridine
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Solomon Derese

1
HN

2,3-Dihydroazepine

2,5-Dihydroazepine
SCH 402

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When numbering give priority to saturated atoms
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Solomon Derese

SCH 402

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Revision

Hetreroatom
O
Type (Z) - Prefix
N
Size (n) - Suffix
Nature of ring - Ending S
P

Prefix
Oxa
Aza
Thia
Phospha

Ring size Saturated

Unsaturated Saturated (With Nitrogen)

3
-irane
4
-etane
5
-olane
6
-inane
7
-epane
8
-ocane
9
-onane
10
-ecane
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Solomon Derese

SCH 402

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Two or more similar atoms contained in a ring are
indicated by the prefixes ‘di-’, ‘tri’, etc
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Solomon Derese

1,3-Thiazole
(Thiazole)

3-chloro-5-methyl-1,2,4-oxadiazole
SCH 402

30

Priority of heteroatoms for numbering purposes:
Highest

B
Lowest

C

N

O

P

S
Se

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As a result the position of
the substituent plays no part in determining
how the ring is numbered in such
compounds
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Solomon Derese

SCH 402

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II
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O

H
N

Furan

Pyrrole

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Solomon Derese

O

Coumarin
SCH 402

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1,4-Dihydropyridine 2,3-Dihydropyridine

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, according to the number of systems,
and the bonding is indicated as follows:
1
2

1
2’

2’

3’’

2

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,
starting from the atom numbered 1
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c
d
b

e
a

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The prefix in
such names has the ending ‘o’, i
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, benzo,
naphtho and so on
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Solomon Derese

SCH 402

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d
c

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1

2

HN

N

1
N
N2

3-Ethyl-5-methylpyrazole
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Solomon Derese

SCH 402

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Heterocycles with maximum number of double bonds
which can be arranged in more than one way
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The numerals indicate the position of
these atoms having the extra hydrogen atom
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Solomon Derese

SCH 402

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Dr
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The Replacement Nomenclature
In
replacement
nomenclature,
the
heterocycle's name is composed of the
carbocycle's name and a prefix that denotes
the heteroatom
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Notice that heterocyclic rings are numbered so
that the heteroatom has the lowest possible
number
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Solomon Derese

SCH 402

46

N

NH
2-Methylazacyclohexane
or

N-Ethylazacyclopentane

2-Methylpiperidine

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Solomon Derese

SCH 402

48



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