Subsections of Chemistry
Organic
Subsections of Organic
IUPAC Naming
IUPAC Naming System
Naming organic compounds using the IUPAC system follows four key steps:
- Identify the main functional group and assign it the highest priority.
- Find the longest carbon chain that includes this group, numbering it to give the lowest possible number to the priority group.
- List and number any substituents (branches), arranging them alphabetically in the name.
- Specify stereochemistry if applicable (E/Z, R/S, cis/trans, etc.).
The final IUPAC name follows this structure:
# - Stereochemistry - # - Prefix F.G(s). - # - Substituent(s) - Parent Chain - Multiple Bond - Suffix F.G.| Component | Description | Example |
|---|---|---|
| Stereochemistry | Spatial orientation (E/Z, R/S, D/L, +/- etc.) | (E)-, (S)-, (-)-, (D)- |
| Prefix (Functional Groups) | Lower priority groups (prefix form) | hydroxy-, oxo-, amino- |
| Substituents | Branched groups, listed alphabetically | 2-methyl, 3-ethyl |
| Parent Chain | Longest continuous chain (homologous series) | pentane, hexane |
| Multiple Bonds | Position & type of double/triple bonds | 2-ene, 3-yne |
| Suffix (Functional Group) | Highest ranking group (based on priority order) | -ol, -one, -oic acid |
Examples of IUPAC naming:
- (E)-4-Hydroxy-3-methylpent-2-en-1-one
- (R)-3,4-Dihydroxy-5-methylcyclohex-2-en-1-one
- (Z)-4-Bromo-3-methylhex-2-en-1-ol
- (S)-2,5-Diamino-3-hydroxy-4-methylhexanoic acid
- (E)-5-Ethyl-4-hydroxy-3,6-dimethylhept-2-en-1-one
- (R,E)-3,5-Dimethoxy-4-methylhex-2-enal
- (S)-4-Ethyl-2-hydroxy-3,5-dimethylhexanoic acid
- (E)-2-Bromo-5-ethyl-4-methylhex-2-enamide
- (Z)-3,6-Dihydroxy-4,8-dimethylundec-2-enoic acid
This method applies to all organic compounds.
Prefix Table (Carbon Chain)
| Carbon Count | Prefix | Condensed Structural Formula | State at Room Temp |
|---|---|---|---|
| 1 | Meth- | $\ce{CH4}$ | Gas |
| 2 | Eth- | $\ce{CH3CH3}$ | Gas |
| 3 | Prop- | $\ce{CH3CH2CH3}$ | Gas |
| 4 | But- | $\ce{CH3CH2CH2CH3}$ | Gas |
| 5 | Pent- | $\ce{CH3CH2CH2CH2CH3}$ | Liquid |
| 6 | Hex- | $\ce{CH3(CH2)4CH3}$ | Liquid |
| 7 | Hept- | $\ce{CH3(CH2)5CH3}$ | Liquid |
| 8 | Oct- | $\ce{CH3(CH2)6CH3}$ | Liquid |
| 9 | Non- | $\ce{CH3(CH2)7CH3}$ | Liquid |
| 10 | Dec- | $\ce{CH3(CH2)8CH3}$ | Liquid |
| 11 | Undec- | $\ce{CH3(CH2)9CH3}$ | Liquid |
| 12 | Dodec- | $\ce{CH3(CH2)10CH3}$ | Liquid |
| 13 | Tridec- | $\ce{CH3(CH2)11CH3}$ | Liquid |
| 14 | Tetradec- | $\ce{CH3(CH2)12CH3}$ | Liquid |
| 15 | Pentadec- | $\ce{CH3(CH2)13CH3}$ | Liquid |
| 16 | Hexadec- | $\ce{CH3(CH2)14CH3}$ | Solid |
| 17 | Heptadec- | $\ce{CH3(CH2)15CH3}$ | Solid |
| 18 | Octadec- | $\ce{CH3(CH2)16CH3}$ | Solid |
| 19 | Nonadec- | $\ce{CH3(CH2)17CH3}$ | Solid |
| 20 | Icos- | $\ce{CH3(CH2)18CH3}$ | Solid |
Suffix Table (Bond Types)
| Bond Type | Suffix | General Formula | Hybridization |
|---|---|---|---|
| Single bond (Alkane) | -ane | $\ce{C_{n} H_{n+2}}$ | $sp^3$ |
| Double bond (Alkene) | -ene | $\ce{C_{n} H_{n}}$ | $sp^2$ |
| Triple bond (Alkyne) | -yne | $\ce{C_{n} H_{n-2}}$ | $sp$ |
Functional Groups
The below table is in decreasing order of priority.
| Functional Group Name | Formula | Prefix (If Substituent) | Suffix (If Principal Group) | General Formula | Key Notes |
|---|---|---|---|---|---|
| Carboxylic Acid | $\ce{-COOH}$ | Carboxy- | -oic acid | $\ce{R-COOH}$ | Highest priority, always at the end. |
| Sulfonic Acid | $\ce{-SO3H}$ | Sulfo- | -sulfonic acid | $\ce{R-SO3H}$ | Strong acid, highly polar. |
| Ester | $\ce{-COO-R}$ | Alkoxycarbonyl- | -oate | $\ce{R-COO-R'}$ | Name alkyl group first, then parent chain. |
| Acid Halide | $\ce{-COX}$ | Halocarbonyl- | -oyl halide | $\ce{R-COX}$ | Named like carboxylic acids. |
| Amide | $\ce{-CONH2}$ | Carbamoyl- / Amido- | -amide | $\ce{R-CONH2}$ | Forms strong hydrogen bonds. |
| Nitrile | $\ce{-CN}$ | Cyano- | -nitrile | $\ce{R-CN}$ | Triple bond, high dipole moment. |
| Aldehyde | $\ce{-CHO}$ | Formyl- / Oxo- | -al | $\ce{R-CHO}$ | Always at the end of chain, no number needed. |
| Thioaldehyde | $\ce{-CHS}$ | Thioformyl- / Thioxo- | -thial | $\ce{R-CHS}$ | Always at the end of chain, no number needed. |
| Ketone | $\ce{-CO-}$ | Oxo- | -one | $\ce{R-CO-R'}$ | Must number position in chain. |
| Thioketone | $\ce{-CS-}$ | Sulfanylidene- | -thione | $\ce{R-CS-R'}$ | Must number position in chain. |
| Alcohol | $\ce{-OH}$ | Hydroxy- | -ol | $\ce{R-OH}$ | Higher priority than alkanes. |
| Thiol | $\ce{-SH}$ | Mercapto- / Sulfanyl- | -thiol | $\ce{R-SH}$ | Less polar than alcohols. |
| Amine | $\ce{-NH2}$ | Amino- | -amine | $\ce{R-NH2}$ | Basic in nature, named like alcohols. |
| Imine | $\ce{=NH}$ | Imino- | -imine | $\ce{R=NH}$ | Basic in nature, named like alcohols. |
| Ether | $\ce{-O-}$ | Alkoxy- | (Uses common names) | $\ce{R-O-R'}$ | Named as alkoxyalkanes. |
| Alkene | $\ce{-C=C-}$ | Alkenyl- | -ene | $\ce{R-C=C-R'}$ | Lowest number to double bond. |
| Alkyne | $\ce{-C#C-}$ | Alkynyl- | -yne | $\ce{R-C#C-R'}$ | Triple bond takes priority over alkanes. |
| Alkane | $\ce{-C-C-}$ | Alkyl- | -ane | $\ce{R-C-C-R'}$ | No functional group, least priority. |
| Halogen | $\ce{-X}$ ($\ce{F, Cl, Br, I}$) | Fluoro-, Chloro-, Bromo-, Iodo- | (Treated as substituent) | $\ce{R-X}$ | Gets lowest number possible. |
| Nitro | $\ce{-NO2}$ | Nitro- | (Treated as substituent) | $\ce{R-NO2}$ | Always gets lowest number possible. |
Additional Naming Rules & Notes
Multiple Functional Groups:
The highest priority group gets the suffix.
All other functional groups are named as prefixes.
Example 1:
- Compound: $\ce{CH3CH(OH)CH2COOH}$
- IUPAC Name: 3-Hydroxybutanoic acid
- Priority Order: Carboxyl ($\ce{-COOH}$) > Hydroxyl ($\ce{-OH}$)
Example 2:
- Compound: $\ce{CH3CH(Br)CH(OH)CH3}$
- IUPAC Name: 2-Bromo-butan-3-ol
- Priority Order: Hydroxyl ($\ce{-OH}$) > Halo ($\ce{-Br}$)
Numbering of Chains:
- The longest continuous chain is chosen.
- The functional group gets the lowest possible number.
Multiple Bonds (Double & Triple):
- If both double $\ce{C=C}$ and triple $\ce{C#C}$ bonds are present, the double bond is given priority in numbering.
Cyclic Compounds:
- Prefix: Cyclo-
- Example: Cyclohexanol → $\ce{C6H11OH}$.
Exceptions & Special Cases
1. Common Names Used
Some compounds have retained their common names as IUPAC-approved names.
| Common Name | IUPAC Name | Formula | Category | Key Notes |
|---|---|---|---|---|
| Formic Acid | Methanoic Acid | $\ce{HCOOH}$ | Carboxylic Acid | Simplest carboxylic acid. |
| Acetic Acid | Ethanoic Acid | $\ce{CH3COOH}$ | Carboxylic Acid | Vinegar’s main component. |
| Propionic Acid | Propanoic Acid | $\ce{CH3CH2COOH}$ | Carboxylic Acid | Name means “first fat” (Greek). |
| Butyric Acid | Butanoic Acid | $\ce{CH3CH2CH2COOH}$ | Carboxylic Acid | Found in rancid butter. |
| Acetone | Propanone | $\ce{CH3COCH3}$ | Ketone | Used as a solvent. |
| Benzaldehyde | Benzenecarbaldehyde | $\ce{C6H5CHO}$ | Aldehyde | Almond-like smell. |
| Toluene | Methylbenzene | $\ce{C6H5CH3}$ | Aromatic Hydrocarbon | Common solvent. |
| Xylene | Dimethylbenzene | $\ce{C6H4(CH3)2}$ | Aromatic Hydrocarbon | Exists as ortho, meta, para. |
| Phenol | Hydroxybenzene | $\ce{C6H5OH}$ | Alcohol/Aromatic | Antiseptic, acidic. |
| Aniline | Aminobenzene | $\ce{C6H5NH2}$ | Amine/Aromatic | Used in dyes. |
| Glycerol | Propane-1,2,3-triol | $\ce{C3H8O3}$ | Alcohol | Found in fats and oils. |
2. Modified Functional Groups Naming
Some groups have unique suffixes or prefixes in IUPAC.
| Functional Group | Common Prefix | IUPAC Suffix | Example | Formula |
|---|---|---|---|---|
| Aldehyde ($\ce{-CHO}$) | Formyl- / Oxo- | -al | Propanal | $\ce{CH3CH2CHO}$ |
| Ketone ($\ce{-CO-}$) | Oxo- | -one | Butanone | $\ce{CH3COCH2CH3}$ |
| Amide ($\ce{-CONH2}$) | Carbamoyl- / Amido- | -amide | Ethanamide | $\ce{CH3CONH2}$ |
| Ester ($\ce{-COO-R}$) | Alkoxycarbonyl- | -oate | Methyl ethanoate | $\ce{CH3COOCH3}$ |
| Nitrile ($\ce{-CN}$) | Cyano- | -nitrile | Propanenitrile | $\ce{CH3CH2CN}$ |
3. Aromatic System Naming Exceptions
Some aromatic compounds have special historical names.
| Common Name | IUPAC Name | Formula | Key Notes |
|---|---|---|---|
| Toluene | Methylbenzene | $\ce{C6H5CH3}$ | Simplest alkylbenzene. |
| Aniline | Aminobenzene | $\ce{C6H5NH2}$ | Aromatic amine. |
| Phenol | Hydroxybenzene | $\ce{C6H5OH}$ | More acidic than alcohols. |
| Benzoic Acid | Benzenecarboxylic Acid | $\ce{C6H5COOH}$ | Simple aromatic acid. |
| Styrene | Phenylethene | $\ce{C6H5CH=CH2}$ | Used in plastics. |
4. Special Aliphatic Naming Exceptions
Some chains do not follow usual alkane naming.
| Common Name | IUPAC Name | Formula | Category |
|---|---|---|---|
| Isopropyl Alcohol | Propan-2-ol | $\ce{CH3CHOHCH3}$ | Alcohol |
| Acetylene | Ethyne | $\ce{C2H2}$ | Alkyne |
| Ethylene | Ethene | $\ce{C2H4}$ | Alkene |
| Isobutane | 2-Methylpropane | $\ce{CH3CH(CH3)CH3}$ | Branched Alkane |
| Isopentane | 2-Methylbutane | $\ce{CH3CH(CH3)CH2CH3}$ | Branched Alkane |
| Neopentane | 2,2-Dimethylpropane | $\ce{C(CH3)4}$ | Highly Branched Alkane |
6. Special Amino Acid Naming
Amino acids often do not follow usual amine and acid naming.
| Common Name | IUPAC Name | Formula | Key Notes |
|---|---|---|---|
| Glycine | 2-Aminoethanoic Acid | $\ce{NH2CH2COOH}$ | Simplest amino acid. |
| Alanine | 2-Aminopropanoic Acid | $\ce{CH3CH(NH2)COOH}$ | Nonpolar. |
| Serine | 2-Amino-3-hydroxypropanoic Acid | $\ce{CH2OHCH(NH2)COOH}$ | Contains hydroxyl group. |
7. Special Oxoacid Naming
Some oxoacids have irregular naming.
| Common Name | IUPAC Name | Formula | Category |
|---|---|---|---|
| Sulfuric Acid | Dihydrogen Sulfate | $\ce{H2SO4}$ | Strong Acid |
| Nitric Acid | Hydrogen Nitrate | $\ce{HNO3}$ | Strong Acid |
| Phosphoric Acid | Trihydrogen Phosphate | $\ce{H3PO4}$ | Weak Acid |
Key Takeaways
- Some common names are still IUPAC-approved (e.g. acetone, toluene, glycerol).
- Carboxylic acids and esters retain some historical names.
- Aromatic compounds often have non-systematic names.
- Amino acids and oxoacids follow special conventions.