Appendix H — IUPAC Nomenclature Quick Reference
Working reference for naming organic compounds. Ch 4 introduces these rules; this appendix is dense lookup. Most recent recommendations: IUPAC (2013) Nomenclature of Organic Chemistry — Recommendations and Preferred Names.
1. The 5 rules of IUPAC nomenclature
- Identify the parent chain. Longest continuous chain containing the principal characteristic group (suffix). For rings vs. chains, choose whichever gives the highest-priority suffix; ties go to the longer.
- Number the parent chain to give the lowest locant to the principal characteristic group. Then in order: lowest locants to multiple bonds, then to substituents as a set, then to the first cited substituent alphabetically.
- Identify substituents and prefix them as
locant-substituent-. Multiple identical: di-, tri-, tetra- (not counted in alphabetization). - Alphabetize substituents in the final name (ignoring multiplicative prefixes; treat iso-, neo- as part of the name letter; treat sec-, tert- as italicized and ignore in alphabetization).
- Lowest locant set rule. When multiple numbering choices give the same locant for the suffix, choose the set that gives the lowest locants summed pairwise first-difference. Then alphabetical first.
2. Principal characteristic group priority (for suffix selection)
| Rank | Group | Suffix | Prefix (if not principal) |
|---|---|---|---|
| 1 | Cation (R₃N⁺) | -aminium | — |
| 2 | Carboxylic acid -COOH | -oic acid (-carboxylic acid for cyclic) | carboxy- |
| 3 | Carboxylic anhydride | -oic anhydride | — |
| 4 | Ester -COOR' | -oate | (alkoxycarbonyl)- |
| 5 | Acyl halide -COX | -oyl halide | halocarbonyl- |
| 6 | Amide -CONR₂ | -amide | carbamoyl- / -carboxamide |
| 7 | Nitrile -CN | -nitrile | cyano- |
| 8 | Aldehyde -CHO | -al / -carbaldehyde | oxo- (when =O) |
| 9 | Ketone >C=O | -one | oxo- |
| 10 | Alcohol -OH | -ol | hydroxy- |
| 11 | Amine -NH₂ | -amine | amino- |
| 12 | Ether R-O-R | (parent on larger side) | alkoxy- |
| 13 | Alkene C=C | -ene | (within parent) |
| 14 | Alkyne C≡C | -yne | (within parent) |
| 15 | Halide R-X | (never suffix) | halo- |
Only the highest-priority group gets the suffix; all others become prefixes. Halides and alkyl groups are always prefixes — they never take suffix priority.
3. Parent hydrocarbon chains
| n | Alkane | Alkene | Alkyne |
|---|---|---|---|
| 1 | methane | — | — |
| 2 | ethane | ethene | ethyne |
| 3 | propane | propene | propyne |
| 4 | butane | butene | butyne |
| 5 | pentane | pentene | pentyne |
| 6 | hexane | hexene | hexyne |
| 7 | heptane | heptene | heptyne |
| 8 | octane | octene | octyne |
| 9 | nonane | nonene | nonyne |
| 10 | decane | decene | decyne |
| 11 | undecane | undecene | undecyne |
| 12 | dodecane | dodecene | dodecyne |
| 15 | pentadecane | ||
| 20 | icosane | ||
| 30 | triacontane |
Rings: cyclo- prefix (cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane).
4. Substituent prefixes (~50 common, alphabetized)
| Prefix | Group | Prefix | Group |
|---|---|---|---|
| acetamido- | -NH-COCH₃ | hydroxy- | -OH |
| acetoxy- | -O-COCH₃ | imino- | =NH |
| acetyl- | -COCH₃ | iodo- | -I |
| allyl- | -CH₂-CH=CH₂ | isobutyl- | -CH₂-CH(CH₃)₂ |
| amino- | -NH₂ | isopropyl- (1-methylethyl) | -CH(CH₃)₂ |
| benzoyl- (Bz) | -C₆H₅-CO- | mercapto- (sulfanyl) | -SH |
| benzyloxy- | -O-CH₂-C₆H₅ | methoxy- | -OCH₃ |
| benzyl- (Bn) | -CH₂-C₆H₅ | methyl- | -CH₃ |
| bromo- | -Br | neopentyl- | -CH₂-C(CH₃)₃ |
| t-butoxy- | -OC(CH₃)₃ | nitro- | -NO₂ |
| n-butyl- | -CH₂CH₂CH₂CH₃ | nitroso- | -N=O |
| sec-butyl- | -CH(CH₃)CH₂CH₃ | oxo- | =O |
| tert-butyl- | -C(CH₃)₃ | pentyl- (amyl-) | -C₅H₁₁ |
| carbamoyl- | -CONH₂ | phenoxy- | -O-C₆H₅ |
| carboxy- | -COOH | phenyl- (Ph) | -C₆H₅ |
| chloro- | -Cl | propargyl- | -CH₂-C≡CH |
| cyano- | -CN | n-propyl- | -CH₂CH₂CH₃ |
| diazo- | =N⁺=N⁻ | silyl- (-SiH₃) / trimethylsilyl- (TMS) | -Si(CH₃)₃ |
| ethoxy- | -OCH₂CH₃ | sulfo- | -SO₃H |
| ethyl- | -CH₂CH₃ | thio- (sulfanyl-) | -S- |
| fluoro- | -F | thiocyanato- | -SCN |
| formyl- | -CHO | tolyl- (methylphenyl-) | -C₆H₄CH₃ |
| hydrazino- | -NHNH₂ | vinyl- (ethenyl-) | -CH=CH₂ |
Multiplier prefixes (not alphabetized): di- (2), tri- (3), tetra- (4), penta- (5), hexa-, hepta-, octa-, nona-, deca-. Use bis-, tris-, tetrakis- for complex substituents to avoid ambiguity (e.g., bis(2-chloroethyl)).
5. Stereochemistry naming
R/S (Cahn-Ingold-Prelog)
- Rank four substituents at chiral C by CIP priority (1 = highest atomic number first; tie at first atom → look at next sphere; double bond = duplicated atom).
- Orient lowest-priority group (usually H) pointing away.
- 1→2→3 clockwise = R; counterclockwise = S.
Prefix to name with locant: (2R)-, (2R,3S)-, etc.
E/Z (around C=C)
- Apply CIP at each sp² C of the double bond.
- Higher-priority groups on same side = Z (zusammen); opposite = E (entgegen).
- Prefix: (2E)-, (3Z)-, etc.
cis/trans
- For disubstituted alkenes where each C has one H and one non-H, cis/trans is unambiguous.
- For rings (esp. cyclohexane): refers to relative position of two substituents on same/opposite face.
- Avoid cis/trans for tri- and tetrasubstituted alkenes — use E/Z.
Meso, racemic, enantiopure
- Meso: contains chirality centers but possesses an internal mirror plane — achiral overall. Written without R/S enantiomer designator, or "(2R,3S)-meso-".
- Racemic: (±)- or rac- or (RS)- prefix; equimolar enantiomers.
- (R)- or (S)- alone = enantiopure (or enriched, with %ee noted).
syn/anti, threo/erythro
- syn / anti: positions of two non-H substituents on adjacent sp³ Cs in an extended (zigzag) drawing — same side or opposite side.
- threo / erythro: older Fischer-projection terms. erythro = same-side in Fischer (like erythrose); threo = opposite (like threose). Modern usage prefers syn/anti.
D/L (sugars, amino acids)
Fischer projection orientation: -OH (sugars) or -NH₂ (AAs) on the bottom chiral center — right = D, left = L. Almost all natural sugars are D, natural amino acids L (cysteine is the wrinkle: L-Cys is (R) due to priority swap).
6. Ring systems
Monocyclic
- cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane.
- Cycloalkenes/-ynes follow same pattern (cyclohexene, cyclohexa-1,3-diene).
Fused bicyclics — von Baeyer naming
Format: bicyclo[x.y.z]alkane where x ≥ y ≥ z = number of carbons between bridgeheads (not counting bridgeheads themselves).
- decalin = bicyclo[4.4.0]decane
- norbornane = bicyclo[2.2.1]heptane
- bicyclo[2.2.2]octane ("BCO")
Number starting at one bridgehead, longest bridge first, then second-longest, then shortest. Substituents get lowest locants by the usual rule.
Spiro
spiro[x.y]alkane — single shared atom; x ≤ y are the carbon counts of the two rings excluding the shared atom.
- spiro[4.5]decane = a cyclopentane and a cyclohexane sharing one atom.
Polycyclic (3+ fusions)
tricyclo[x.y.z.aᵇ,ᶜ]alkane — superscript locants specify the secondary bridge endpoints. adamantane = tricyclo[3.3.1.1³,⁷]decane.
Common ring names retained
- adamantane, norbornane, cubane, prismane, decalin, hydrindane, indane, tetralin, fluorene, indene, acenaphthylene.
7. Heterocycle naming (Hantzsch-Widman + retained names)
| Structure | Retained name | Position numbering |
|---|---|---|
| 5-ring, 1 N | pyrrole | N=1, then α=2,3, β=3,4 |
| 5-ring, 1 O | furan | O=1 |
| 5-ring, 1 S | thiophene | S=1 |
| 5-ring, 1 N + 1 O | oxazole / isoxazole | O=1, N=3 / O=1, N=2 |
| 5-ring, 1 N + 1 S | thiazole / isothiazole | similar |
| 5-ring, 2 N (1,3) | imidazole | N=1, N=3 |
| 5-ring, 2 N (1,2) | pyrazole | N=1, N=2 |
| 5-ring, 3 N | 1,2,3- or 1,2,4-triazole | per locant |
| 5-ring, 4 N | tetrazole | N=1-4 |
| 6-ring, 1 N | pyridine | N=1 |
| 6-ring, 1 O | 2H- or 4H-pyran | O=1 |
| 6-ring, 2 N (1,3) | pyrimidine | N=1, N=3 |
| 6-ring, 2 N (1,4) | pyrazine | N=1, N=4 |
| 6-ring, 2 N (1,2) | pyridazine | N=1, N=2 |
| 6-ring, 3 N | triazine | per locant |
| Benzo-fused 5N | indole / benzimidazole | N=1, fused at 2,3 |
| Benzo-fused 6N | quinoline / isoquinoline | N=1 / N=2 |
| Purine | (pyrimidine + imidazole fusion) | 9 atoms, N1, N3, N7, N9 |
| Pteridine | (pyrimidine + pyrazine fusion) | N1, N3, N5, N8 |
For Hantzsch-Widman systematic naming of heterocycles not on this list, combine prefixes (oxa-, aza-, thia-, etc.) with size/saturation stems (-irine, -etidine, -olane, -inane, etc.).
8. Aromatic naming
Benzene derivatives
| Substituent | Common name (retained) |
|---|---|
| -CH₃ | toluene |
| -OH | phenol |
| -NH₂ | aniline |
| -COOH | benzoic acid |
| -CHO | benzaldehyde |
| -CO-CH₃ | acetophenone |
| -OCH₃ | anisole |
| -CH=CH₂ | styrene |
| -CH(CH₃)₂ | cumene |
| 1,3,5-(CH₃)₃ | mesitylene |
| -SO₃H | benzenesulfonic acid |
ortho / meta / para
- ortho- (o-) = 1,2; meta- (m-) = 1,3; para- (p-) = 1,4.
- Modern IUPAC prefers numerical locants in PINs (preferred IUPAC names): 1,4-dichlorobenzene rather than p-dichlorobenzene. Both still accepted.
Multiple substituents
- If a retained name (toluene, phenol, aniline) is used, the substituent fixing that name takes position 1.
- Number to give lowest locants to all other substituents.
- Alphabetize substituents in the name.
Polycyclic aromatics
Naphthalene (numbered 1-8 around periphery), anthracene (1-10), phenanthrene (1-10), pyrene, fluorene, indene, azulene. Substituent positions follow each system's conventional numbering.
9. Carbohydrate naming
D/L assignment
Fischer projection, longest carbon chain vertical, most oxidized C at top. The configuration of the highest-numbered chiral center (penultimate C; C5 in hexoses) determines D (OH right) or L (OH left).
Anomers (α/β)
- Cyclic sugar — the anomeric carbon (C1 in aldoses, C2 in ketoses) is sp³ after ring closure.
- α: -OH at anomeric C down in standard Haworth projection (trans to CH₂OH reference); β: -OH up (cis).
- For D-sugars: α = anomeric OH on opposite side to D-defining group; β = same side.
Ring sizes
- pyranose: 6-membered (5C + O)
- furanose: 5-membered (4C + O)
Common sugars
| Sugar | Type | D/L | Common form |
|---|---|---|---|
| D-glucose | aldohexose | D | α/β-D-glucopyranose |
| D-fructose | ketohexose | D | β-D-fructofuranose |
| D-galactose | aldohexose | D | α/β-D-galactopyranose |
| D-mannose | aldohexose | D | α/β-D-mannopyranose |
| D-ribose | aldopentose | D | β-D-ribofuranose |
| 2-deoxy-D-ribose | aldopentose | D | β-D-2-deoxyribofuranose |
| D-xylose | aldopentose | D | α/β-D-xylopyranose |
| L-arabinose | aldopentose | L | α/β-L-arabinofuranose |
Disaccharide nomenclature: link glycoside oxygen letters, e.g., α-D-Glcp-(1→4)-α-D-Glcp = maltose.
10. Amino acid naming
20 proteinogenic amino acids. All are L in proteins (S configuration except L-cysteine, which is R because S has higher CIP priority than COOH). Three-letter and one-letter codes:
| Name | 3-letter | 1-letter | R-group (side chain) |
|---|---|---|---|
| Alanine | Ala | A | -CH₃ |
| Arginine | Arg | R | -(CH₂)₃-NH-C(=NH)NH₂ |
| Asparagine | Asn | N | -CH₂-CONH₂ |
| Aspartic acid | Asp | D | -CH₂-COOH |
| Cysteine | Cys | C | -CH₂-SH |
| Glutamic acid | Glu | E | -(CH₂)₂-COOH |
| Glutamine | Gln | Q | -(CH₂)₂-CONH₂ |
| Glycine | Gly | G | -H (achiral) |
| Histidine | His | H | -CH₂-imidazole |
| Isoleucine | Ile | I | -CH(CH₃)CH₂CH₃ |
| Leucine | Leu | L | -CH₂CH(CH₃)₂ |
| Lysine | Lys | K | -(CH₂)₄-NH₂ |
| Methionine | Met | M | -(CH₂)₂-S-CH₃ |
| Phenylalanine | Phe | F | -CH₂-Ph |
| Proline | Pro | P | (cyclic, NH ring) |
| Serine | Ser | S | -CH₂-OH |
| Threonine | Thr | T | -CH(OH)CH₃ |
| Tryptophan | Trp | W | -CH₂-indol-3-yl |
| Tyrosine | Tyr | Y | -CH₂-(p-OH-Ph) |
| Valine | Val | V | -CH(CH₃)₂ |
Peptides written N→C with single letters or three-letter abbreviations separated by hyphens: H-Gly-Ala-Phe-OH = GAF.
11. Retained common names (allowed by IUPAC)
| Common name | Systematic (PIN) |
|---|---|
| acetic acid | ethanoic acid |
| acetone | propan-2-one |
| acetaldehyde | ethanal |
| acetylene | ethyne |
| acrylic acid | prop-2-enoic acid |
| allyl alcohol | prop-2-en-1-ol |
| anisole | methoxybenzene |
| benzaldehyde | benzenecarbaldehyde |
| benzoic acid | benzenecarboxylic acid |
| cumene | (1-methylethyl)benzene |
| ethylene | ethene |
| ethylene glycol | ethane-1,2-diol |
| formaldehyde | methanal |
| formic acid | methanoic acid |
| glycerol | propane-1,2,3-triol |
| isobutyl- | 2-methylpropyl- |
| isopropyl- | propan-2-yl- |
| mesitylene | 1,3,5-trimethylbenzene |
| neopentyl- | 2,2-dimethylpropyl- |
| oxalic acid | ethanedioic acid |
| phenol | benzenol (not used) |
| propylene | propene |
| sec-butyl- | butan-2-yl- |
| styrene | phenylethene |
| tert-butyl- | (1,1-dimethylethyl)- |
| toluene | methylbenzene |
| vinyl- | ethenyl- |
| xylene (o,m,p) | (di)methylbenzene |
IUPAC 2013 permits all of these in general nomenclature but specifies the systematic name as the Preferred IUPAC Name (PIN) for regulatory/database use.
12. Greek letters in nomenclature
- α (alpha): the C adjacent to a functional group (α-carbon of COOH, α-bromoketone).
- β (beta): two carbons away (β-hydroxy ketone, β-keto ester).
- γ (gamma): three carbons away (γ-butyrolactone).
- δ (delta): four carbons (δ-valerolactone).
- ω (omega): the terminal carbon (ω-3 fatty acids: double bond 3 carbons from terminal end).
- ortho/meta/para: 1,2-, 1,3-, 1,4- on benzene (Section 8).
- α/β for anomers (Section 9).
- D/L vs R/S: D/L is configurational (Fischer-projection-based, family relationships); R/S is absolute (CIP-based, single center).
13. Worked examples (mixed difficulty)
Structure → Name
- CH₃-CH₂-CH₂-OH → propan-1-ol (or 1-propanol; common: n-propanol).
- (CH₃)₂CH-CH(Cl)-CH₃ → 2-chloro-3-methylbutane.
- CH₃-CH=CH-CH₂-CHO → (2E)-pent-2-enal (number to give -CHO C1).
- HOOC-CH₂-CH(NH₂)-COOH → 2-aminobutanedioic acid (aspartic acid); the L-enantiomer is L-Asp.
- (CH₃)₃C-O-CH₃ → 2-methoxy-2-methylpropane (MTBE).
- C₆H₅-CO-NH₂ → benzamide.
- CH₂=CH-CH(OH)-CH₃ → but-3-en-2-ol (number to give -OH lowest, 2 < 3).
- Cyclohexane with -CH₃ at 1 and -OH at 3, cis → cis-3-methylcyclohexan-1-ol; (1R,3S)- if pure enantiomer; (1S,3R)- for the other.
- HOCH₂-CH(OH)-CHO → 2,3-dihydroxypropanal (glyceraldehyde); D-glyceraldehyde = (R)-(+)-glyceraldehyde.
- A 6-membered N-containing ring with 2 N (1,4) = pyrazine.
Name → Structure
- (2R,3S)-2-bromo-3-chlorobutane → CH₃-C(Br)H-C(Cl)H-CH₃, with the indicated stereo.
- 3-methylpent-2-en-4-yn-1-ol → HC≡C-C(CH₃)=CH-CH₂-OH (with C1 the CH₂OH).
- β-D-glucopyranose → 6-membered glucose with anomeric -OH up (Haworth), all other -OH per glucose configuration.
- N,N-dimethylformamide (DMF) → HCO-N(CH₃)₂.
- 1-phenylethan-1-one → C₆H₅-CO-CH₃ (acetophenone).
- bicyclo[2.2.1]hept-2-ene → norbornene (C₇H₁₀, one C=C in the larger bridge).
- (S)-(+)-2-methylbutan-1-ol → CH₃-CH₂-C*(H)(CH₃)-CH₂OH, (S) at C2.
- 3-oxobutanoic acid → CH₃-CO-CH₂-COOH (acetoacetic acid).
- (2R,3R)-tartaric acid → HOOC-C(OH)H-C(OH)H-COOH (natural / L-(+)-tartaric).
- adamantane-1-carboxylic acid → 1-adamantyl-COOH; the COOH replaces an H on a bridgehead C.
14. Resources
- IUPAC (2013). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names.
- Favre, H. A.; Powell, W. H. (2014). Nomenclature of Organic Chemistry: Recommendations and Preferred Names 2013. RSC.
- ChemDraw / MarvinSketch / RDKit — auto-name structures.
- NCI CIR Resolver (cactus.nci.nih.gov) — free online name ↔ structure.
- OPSIN (opsin.ch.cam.ac.uk) — parses IUPAC name → structure.
Nomenclature is mostly vocabulary. The first hundred molecules feel hard; after that, the rules become reflexive and the exceptions become familiar.