| Type | What Changes | Example (C₄H₁₀) |
|---|---|---|
| Chain | Arrangement of the carbon skeleton (straight vs branched) | Butane vs 2-methylpropane |
| Positional | Position of the functional group on the same chain | Butan-1-ol vs Butan-2-ol |
| Functional group | The functional group itself is different | Ethanol (C₂H₅OH) vs Methoxymethane (CH₃OCH₃) |
Consequences of Structural Isomerism
Structural isomers share the exact same molecular formula but have different physical properties (different boiling points due to surface contact area) and different chemical reactivity (especially functional group isomers like ethanol vs methoxymethane).
Chain Conformation vs True Isomerism
Drawing a straight carbon chain with a bend or 90° angle does NOT create an isomer! Because single C–C sigma bonds rotate freely, conformational rotation produces identical molecules. To form a true isomer, you must disconnect and reconnect atoms in a different order.
Primary (1°), Secondary (2°), and Tertiary (3°) Compounds
Alcohols & Halogenoalkanes: Classified by the number of carbon atoms bonded to the carbon bearing the functional group:
- Primary (1°): Carbon attached to 1 (or 0) other carbon (e.g.
CH₃CH₂OH) - Secondary (2°): Carbon attached to 2 other carbons (e.g.
CH₃CH(OH)CH₃) - Tertiary (3°): Carbon attached to 3 other carbons (e.g.
(CH₃)₃COH)
Amines: Classified by the number of carbons bonded directly to the nitrogen atom.
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