Structural isomers of alkanes C₄–C₇ and boiling points
ChemistryOrganic ChemistryAges 16–17
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Organic Chemistry
Choose the molecular formula C₄H₁₀, C₅H₁₂, C₆H₁₄ or C₇H₁₆ to see all of its structural isomers (2, 3, 5 and 9 compounds) as condensed structural formulas or skeletal formulas, with the parent chain highlighted and numbered. Each isomer comes with its IUPAC name, its primary/secondary/tertiary/quaternary carbons and its real boiling point; a bar chart shows that the more branched the chain, the lower the boiling point. A 3D mode builds a ball-and-stick model of the selected isomer with tetrahedral carbons (109.5°) and every hydrogen atom; rotate it to see the zigzag carbon chain and how compact branched molecules are.
Lesson: Alkanes – structural isomerism, IUPAC nomenclature and physical properties
What it shows
From four carbon atoms upwards, an alkane can arrange its carbon skeleton in more than one way, giving structural (chain) isomers with the same molecular formula but different shapes and properties. The number grows quickly: 2 for C₄H₁₀, 3 for C₅H₁₂, 5 for C₆H₁₄ and 9 for C₇H₁₆. IUPAC names are built on the longest chain, numbered to give the branches the lowest locants. Branching makes molecules more compact, which reduces surface contact and the London (van der Waals) forces between them, so boiling points generally fall as branching increases.
How to use
Click a formula button from C₄H₁₀ to C₇H₁₆ and switch the Formula style between condensed and skeletal. Turn on Highlight and number the parent chain, then tap an isomer, a bar of the chart or a row of the table to read how its name is built and how its boiling point compares with the unbranched isomer. Switch to 3D to rotate a ball-and-stick model, and use Reset view to return to the starting angle.
Parameters you can change
- Number of carbon atoms n (CₙH₂ₙ₊₂) 4–7
- Formula style Condensed structural formula, Skeletal formula
- Highlight and number the parent chain
- Show boiling point chart
Questions to explore
- How many structural isomers does C₆H₁₄ have, and which one contains a quaternary carbon atom?
- Why does pentane boil at 36.1 °C while 2,2-dimethylpropane boils at only 9.5 °C?
- Which C₇H₁₆ isomer breaks the pattern 'more branching, lower boiling point', and why?
