Heterocycles
Chem 6352
Heterocyclic Nomenclature (adapted from: bruckner.chem.uconn.edu/PDFfiles/hetshort.pdf and from
Gilchrist, T. L. Heterocyclic Chemistry; Longman; London, 1992)
The standard method for naming heterocyclic rings is the Hantzsch-Widman nomenclature
system. A heterocycle is a ring containing at least one atom that is not carbon: “hetero” means
“different.” Nitrogen, oxygen, and sulfur are the primary elements seen in common heterocycles.
Heterocycles may be aromatic or not aromatic, but aromatic heterocycles are often called “heteroaryls.”
Names in the Hantzsch-Widman system provide data relating to several categories. First, the
identity of the heteroatom present in the ring is established by the use of different prefixes for each type.
The three prefixes are oxa-, thia-, and aza- for oxygen, sulfur, and nitrogen, respectively. Second,
numbers assigned to the atom denote heteroatom position. Third, the size of the ring and the degree of
unsaturation is described by the suffix at the end.
Table. Common Hantzsch-Widman suffixes.
ring size
unsaturated ring with
only O or S
-irene
-ete
-ole
-ine
-epine
-ocine
-onine
-ecine
3
4
5
6
7
8
9
10
unsaturated ring with N
-irine
-ete
-ole
-ine
-epine
-ocine
-onine
-ecine
saturated ring with only
O or S
-irane
-etane
-olane
-inane (-ane)
-epane
-ocane
-onane
-ecane
saturated ring with N
-iridine
-etidine
-olidine
-inane (-ane)
-epane
-ocane
-onane
-ecane
Examples of ring naming:
H
N
Aziridine:
This ring contains a nitrogen (prefix is aza-) and is a completely saturated three-membered ring
(-iridine). Rings that contain a nitrogen require a designated suffix. When combining the prefixes and
suffixes, two vowels can end up together. In this case that would be azairidine. When this happens,
drop the vowel on the end of the first part.
HN
O
1,2-Oxazetidine:
This ring contains nitrogen (aza-) and oxygen (oxa-) and is a fully saturated four-membered ring
(-etidine). Atom prefixes have a strict order in which they are to be listed. For the three atoms we will
see, the order is oxygen followed by sulfur followed by nitrogen. So, after dropping the appropriate
vowels, we get oxazetidine. Note that if there are two atom prefixes, vowels will be dropped by the
earlier prefix. The numbers are placed in order of the prefixes with priority of the numbers being the
same as the order of the prefixes. Oxygen is in position 1, and nitrogen is in position 2.
N
O
N
1,2,5-Oxadiazole:
This ring has both nitrogen (aza-) and oxygen (oxa-). Unsaturated five-membered rings with
nitrogen have the –ole suffix. The presence of two nitrogens requires a di- in front of aza-. Note that the
ʻaʼ in oxa- is not dropped since there are not two vowels together. Oxygen is higher priority than
nitrogen, so it is in position 1 by default. The two nitrogens are therefore at positions 2 and 5.
O
S
1,3-Oxathiolane:
Prefixes of oxa- and thia- with a suffix of –olane initially gives oxathiolane. Oxygen takes
priority in numbering to give 1,3-oxathiolane.
Not all heterocyclic rings follow the Hantzsch-Widman rules listed above, typically because they have
established common names. These trivial names typically show traces of the systematic nomenclature,
but do not completely follow the rules.
Heterocycles
O
H
N
O
S
H
N
H
N
oxirane/
epoxide
thiirane
aziridine
azirine
O
NH
S
HN
HN
N N
diaziridine
diazirine
thietane
oxetane
azetidine
O
O
S
S
H
N
H
N
H
N
tetrahydrofuran
THF
furan
thiolane
thiophene
pyrrolidine
pyrrole
3-pyrroline
!-lactam
N
2-H-pyrrole
(uncommon)
O
O
O
benzofuran
S
coumaran
dibenzothiophene
benzothiophene
isobenzofuran
O
O
N
H
oxindole
N
H
indoline
N
indole
indolinine
(uncommon)
O
O
N
H
N
H
S
NH
N
N
indolizine
pyrrolizine
N
H
indoxyl
isatin
isoindole
N
H
carbazole
O
O
O
S
S
O
NH
O
NH
O
N
O
N
S
N
N
S
HN
NH
HN
N
HN
N
HN
H
N
N
HN
N
H
N
dioxolane dithiolane oxazolidine oxazolidinone oxazole isoxazole thiazole isothiazole imidazolidine 2-imidazoline imidazole pyrazolidine 2-pyrazoline pyrazole
N
O
O
benzoxazole
O
benzodioxole
O
N
S
N
HN
O
indoxazine
O
O
Tetrahydropyran Dihydropyran
THP
DHP
N
N
H
1H-indazole
N
H
benzimidazole
purine
N
H
N
HN
N
N NH
N N
1,2,3-oxadiazole 1,3,4-thiadiazole 1,2,3-triazole 1,2,4-triazole
O
N
N
S
benzothiazole
N
N
N
N
N
N
N
N
N
N
N N
N
N
H
tetrazole benzotriazole quinuclidine diazabicyclooctane diazabicycloundecane
DBU
DABCO
H
N
O
N
N
N
N
4H-pyran 2H-pyran piperidine pyridine
H
N
N
picoline
N
N
collidine
lutidine
O
pyridone
acridine
O
O
O
O
chromene
O
coumarin
O
isocoumarin
O
O
O
xanthene
S
quinoline
S
S
N
N
S
S
O
N
H
tetrahydroquinoline
S
N
N
N
O
H
quinolone
4H-quinolizine quinolizinium
isoquinoline
H
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
O
S
N
N
O
S
H
H
H
1,4-dioxane morpholine paraformaldehyde 1,4-dithiane 1,3-dithiane thiomorpholine trithiane piperazine pyrazine pyrimidine pyridazine 1,3,5-triazine tetrazine
N
N
N
1,8-naphthyridine
N
quinoxaline
N
N
quinazoline
N
N
N
cinnoline
N
N
N
N
H
!-carboline
phthalazine
N
N
N
bipyridyl
cyclazine
O
N
H
phenoxazine
S
N
H
phenothiazine
N
N
N
N
phenazine
N
O
S
NH
N
pteridine
julolidine
H
N
N
oxepine
thiepin
azepine
benzodiazepine
Examples of Biologically Relevant Heterocycles
O
O
HN
N
NH 2
N
O
N
niacin
nicotine
NH 2
N
N
O
HN
N
H
thymine
O
N
H
uracil
O
N
H
cytosine
N
H 2N
adenine
N
O
N
H
O
N
guanine
N
N
O
N
O
O
caffeine
N
H
N
H
uric acid
NH 2
HO
N
H
NH 2
O
N
H
tryptophan
N
H
serotonin
melatonin
O
Et 2N
N
N
H
N
H
HN
NH
H
N
HN
NH
H
N
N
H
lysergic acid diethyl amide
LSD
porphyrinogen
porphyrin
N
N
melamine
H
N
HN
CO2H
NH 2
H 2N
cyanuric acid
O
N
N
NH 2
NH
O
H
N
HN
HN
N
O
H
N
O
NH 2
NH 2