Organic Chemistry Nomenclature Notes 🧪
Pro Tip for Studying:
Start by memorizing the main functional groups and their suffixes – this is the foundation of organic naming!
Functional Groups and Homologous Series 🧪
Functional Group
An atom or group of atoms attached to a carbon chain that gives organic compounds their characteristic chemical properties.
Examples:
- Hydroxyl group: \( -OH \)
- Aldehyde group: \( -CHO \)
- Carboxylic acid group: \( -COOH \)
Homologous Series
A family of organic compounds with the same functional group.
- Members are called homologues
- Successive members differ by \( -CH_2 \) unit
- Examples: alkanes, alkenes, alkynes, haloalkanes, alcohols
Example: The alkane series: Methane (\( CH_4 \)), Ethane (\( C_2H_6 \)), Propane (\( C_3H_8 \))… each differs by \( -CH_2 \).
IUPAC Nomenclature System 📝
Basic Principles
- Identify the parent hydrocarbon (longest carbon chain)
- Number the chain so substituents get the lowest numbers
- Name substituents as prefixes in alphabetical order
- Indicate positions with numbers separated by hyphens
Naming Alkanes
- Straight-chain alkanes: End with suffix “-ane”
- Prefix indicates number of carbons:
| Carbon Atoms | Name | Formula |
|---|---|---|
| 1 | Methane | \( CH_4 \) |
| 2 | Ethane | \( C_2H_6 \) |
| 6 | Hexane | \( C_6H_{14} \) |
| 8 | Octane | \( C_8H_{18} \) |
Branched Chain Alkanes
- Alkyl groups are carbon branches
- Common alkyl groups:
- Methyl \( (CH_3-) \)
- Ethyl \( (CH_3CH_2-) \)
- Isopropyl \( ((CH_3)_2CH-) \)
- tert-Butyl \( ((CH_3)_3C-) \)
Naming Rules:
- Longest chain = parent name
- Number chain so branches get lowest numbers
- Multiple identical groups: Use di-, tri-, tetra-
- Different groups: List alphabetically
Example:
\( CH_3-CH(CH_3)-CH_2-CH(CH_3)-CH_3 \)
= 2,4-Dimethylpentane ✅
(not 2,4-methylpentane or 3,5-dimethylpentane)
Another Example:
\( CH_3-CH_2-CH(CH_3)-CH(CH_2CH_3)-CH_3 \)
= 3-Methyl-4-ethylhexane
(ethyl comes before methyl alphabetically)
Functional Group Priority 🥇
Order of Priority (Highest to Lowest):
- Carboxylic acid \( (-COOH) \)
- Aldehyde \( (-CHO) \)
- Ketone \( (>C=O) \)
- Alcohol \( (-OH) \)
- Alkene \( (>C=C<) \)
- Alkyne \( (-C≡C-) \)
Naming Compounds with Functional Groups:
- Principal functional group determines suffix
- Other groups become prefixes
- Number chain to give principal group lowest number
Example:
\( HO-CH_2-CH_2-CH_2-C-CH_3 \)
= 5-Hydroxypentan-2-one ✅
(ketone has priority over alcohol)
Another Example:
\( CH_3CH_2C≡C-CH_2-CH=CH_2 \)
= Hept-1-en-5-yne
(alkene gets lower number than alkyne)
Benzene Nomenclature 🌀
Monosubstituted Benzene:
- Substituent + “benzene”
- Common names accepted:
| Compound | Common Name |
|---|---|
| \( C_6H_5CH_3 \) | Toluene |
| \( C_6H_5OCH_3 \) | Anisole |
| \( C_6H_5NH_2 \) | Aniline |
Disubstituted Benzene:
- Use numbers (1,2- 1,3- 1,4-) OR:
- ortho (o-): 1,2-substitution
- meta (m-): 1,3-substitution
- para (p-): 1,4-substitution
Example:
1,3-Dibromobenzene = m-Dibromobenzene
Polysubstituted Benzene:
- Number to give lowest possible numbers
- List substituents alphabetically
Example:
\( \chemfig{*6((=O)-=-N(=O)-=)} \)
= 2-Chloro-1-methyl-4-nitrobenzene ✅
(numbering gives lowest set: 1,2,4)
🚀 NEET High-Yield Concepts 💡
- Functional group identification – Know suffixes/prefixes for all major groups
- IUPAC naming rules – Especially numbering priority and substituent order
- Benzene derivatives – Ortho/meta/para positions and naming conventions
- Homologous series – Recognize patterns and \( -CH_2 \) relationships
- Compound types – Distinguish between alkanes, alkenes, alkynes, and functional derivatives
Exam Tip: Practice naming at least 5 compounds daily – it’s the best way to master these concepts!
