Heterocycles Ring compounds with elements other than carbon in the ring. The most common elements to appear in heterocyclic compounds are oxygen, nitrogen and sulfur.

The aliphatic heterocycles are similar to the open chain analogues, ethers, amines and sulfides.

The aromatic heterocycles are similar to other aromatic compounds.

Heterocyclic Nomenclature

Replacement nomenclature (IUPAC recommended 1957)

Oxygen oxa

Sulfur thia

Nitrogen aza

Lowest number assigned to the hetero atom with the highest precedence: O > S > N

Sthiacyclobutane

ONH

1-oxa-3-azacyclopentane

Hantzsch-Widman method (1888)

Suffixes

O S NH

* oxiraneethylene oxideoxacyclopropane

* thiiraneethylene sulfidethiacyclopropane

* aziridineethylene imineazacyclopropane

NN

N ON

H

diazirane 1-azirine oxaziridineoxazacyclopropane

Some examples, you must know the * names

O S NH

N N

oxetaneoxacyclobutane

thietanethiacyclobutane

azetidineazacyclobutane

azeteazacyclobutadiene

1-azetine1-azacyclobutene

O

O NH

O

O S NH

* furanoxoleoxacyclopentandiene

* thiophenethiolethiacyclopentandiene

* pyrrole

1,3-dioxolane1,3-dioxacyclopentane

* tetrahydrofuran* pyrrolidineazacyclopentane

N

O

N

SON

NH

NN

NH

N

NH

N

pyrazole imidazole 1,2,4-triazole

oxazole isooxazole thiazole

O O O

O

O

NH

NH

HN

O

O

4-hydropyran 2-pyrone 4-pyrone

* 1,4-dioxane * piperidine piperazine

N

N

NN N

N

N NH

O

pyridazine pyrimidine pyrazine

* pyridine * morpholine

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