Heterocyclic Nomenclature and Common Examples

Vocabulary flashcards covering key terms, prefixes, suffixes, rules, and representative heterocycles from the lecture on heterocyclic nomenclature and biologically relevant heterocycles.

Heterocycle

A ring system that contains at least one atom other than carbon (e.g., N, O, S).

Hantzsch-Widman nomenclature

Systematic method for naming heterocycles using heteroatom prefixes, numeric locants, and ring-size/unsaturation suffixes.

Heteroaryl

An aromatic heterocycle or its substituent group.

Prefix oxa-

Denotes the presence of an oxygen atom in the heterocycle.

Prefix thia-

Denotes the presence of a sulfur atom in the heterocycle.

Prefix aza-

Denotes the presence of a nitrogen atom in the heterocycle.

Unsaturated ring (H-W)

Ring containing one or more double bonds; named with suffixes like –ole, –ine, –epine, etc.

Saturated ring (H-W)

Fully hydrogenated ring; named with suffixes like –olane, –inane, –epane, etc.

Suffix ‑irene

3-membered unsaturated ring with O or S only.

Suffix ‑irine

3-membered unsaturated ring containing nitrogen.

Suffix ‑irane

3-membered saturated ring with only O or S.

Suffix ‑iridine

3-membered saturated ring containing nitrogen.

Suffix ‑ete / ‑etane / ‑etidine

Indicates 4-membered rings (unsaturated/saturated, with or without N).

Suffix ‑ole

5-membered unsaturated ring; –ole for O/S or for rings containing N.

Suffix ‑olane

5-membered saturated ring with O or S only.

Suffix ‑olidine

5-membered saturated ring containing nitrogen.

Suffix ‑ine

6-membered unsaturated ring.

Suffix ‑inane (-ane)

6-membered saturated ring.

Suffix ‑epine / ‑epane

7-membered unsaturated (-epine) or saturated (-epane) ring.

Suffix ‑ocine / ‑ocane

8-membered unsaturated (-ocine) or saturated (-ocane) ring.

Suffix ‑onine / ‑onane

9-membered unsaturated (-onine) or saturated (-onane) ring.

Suffix ‑ecine / ‑ecane

10-membered unsaturated (-ecine) or saturated (-ecane) ring.

Vowel-dropping rule

When adjacent vowels arise between prefix and suffix (e.g., aza-irane), delete the final vowel of the prefix.

Prefix priority order

Oxygen > sulfur > nitrogen; determines both prefix order and numeric locants.

Aziridine

Three-membered saturated ring containing nitrogen (aza- + ‑iridine).

1,2-Oxazetidine

Four-membered saturated ring with O at position 1 and N at position 2 (oxa- + aza- + ‑etidine).

1,2,5-Oxadiazole

Five-membered unsaturated ring with O at pos 1 and two nitrogens at pos 2 & 5 (oxa- + diaza- + ‑ole).

1,3-Oxathiolane

Five-membered saturated ring with O at pos 1 and S at pos 3 (oxa- + thia- + ‑olane).

Trivial name

Common, established heterocycle name that does not fully follow Hantzsch-Widman rules (e.g., pyridine).

Oxirane (Epoxide)

Three-membered saturated ring containing oxygen; common name for an epoxide.

Tetrahydrofuran (THF)

Five-membered saturated ring with one oxygen; common laboratory solvent.

Furan

Five-membered unsaturated aromatic ring with one oxygen.

Pyridine

Six-membered aromatic ring with one nitrogen; basic heteroaromatic.

Pyrrole

Five-membered aromatic ring with one NH; weakly basic due to protonated N.

Imidazole

Five-membered aromatic ring with two nitrogens at 1,3-positions.

Indole

Bicyclic system: benzene fused to pyrrole; core of tryptophan and serotonin.

Quinolone

Bicyclic aromatic system (benzene + pyridone) often used as antibiotic scaffold.

Diazabicyclooctane (DABCO)

Rigid bicyclic tertiary diamine used as base and catalyst.

Purine

Fused imidazole-pyrimidine heteroaromatic; core of adenine & guanine.

Adenine

Purine nucleobase; 6-aminopurine found in DNA & RNA.

Guanine

Purine nucleobase; 2-amino-6-oxopurine in DNA & RNA.

Thymine

Pyrimidine nucleobase; 5-methyl-2,4-dioxopyrimidine found in DNA.

Uracil

Pyrimidine nucleobase; 2,4-dioxopyrimidine found in RNA.

Cytosine

Pyrimidine nucleobase; 4-amino-2-oxopyrimidine.

Tryptophan

Essential amino acid containing an indole ring in its side chain.

Caffeine

Trimethylxanthine stimulant; methylated purine derivative.

Serotonin

Neurotransmitter derived from tryptophan; contains indole and primary amine.

Melatonin

Hormone regulating circadian rhythm; acetylated, methoxylated indole.

Lysergic acid diethylamide (LSD)

Psychedelic ergoline with multiple fused heterocycles, including indole.

Porphyrin

Planar macrocycle of four pyrrole units; core of heme and chlorophyll.