Four-carbon naming: double-bond and alcohol positions
Name and draw the complete required unbranched families, including both butenes and the specified primary and secondary alcohol positions.
Extended only (Supplement) · Chemistry 0620, 2026–2028.
Before you begin
- Use the four family suffixes and draw every atom and bond.
- Distinguish a molecular formula from structural isomers.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How many carbons does butanoic acid include?
What you will learn
- Name and draw structural and displayed formulas for required unbranched alkanes, alkenes, alcohols and acids up to four carbons.
- Locate C=C and OH positions using the appropriate lowest position number.
Choose a family, try drawing a named molecule, then open the reference to compare every atom and bond. These are the Extended naming examples; the diagrams show connectivity rather than molecular shape.
Alkanes · 4 structures
Structural formula: CH₄.
Structural formula: CH₃CH₃.
Structural formula: CH₃CH₂CH₃.
Structural formula: CH₃CH₂CH₂CH₃.
Alkenes · 4 structures
Structural formula: CH₂=CH₂.
Structural formula: CH₂=CHCH₃.
Structural formula: CH₂=CHCH₂CH₃.
Structural formula: CH₃CH=CHCH₃.
Alcohols · 6 structures
Structural formula: CH₃OH.
Structural formula: CH₃CH₂OH.
Structural formula: CH₃CH₂CH₂OH.
Structural formula: CH₃CH(OH)CH₃.
Structural formula: CH₃CH₂CH₂CH₂OH.
Structural formula: CH₃CH(OH)CH₂CH₃.
Carboxylic acids · 4 structures
Structural formula: HCOOH.
Structural formula: CH₃COOH.
Structural formula: CH₃CH₂COOH.
Structural formula: CH₃CH₂CH₂COOH.
Count the whole carbon chain and use the family ending
The prefixes meth–, eth–, prop– and but– identify one, two, three and four carbons respectively. The required unbranched alkanes are methane, ethane, propane and butane. The simple alkene family starts at ethene and also includes propene, but-1-ene and but-2-ene. There is no one-carbon C=C alkene. The reference gives structural shorthand and complete displayed drawings for every example.
The required alcohols are methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol and butan-2-ol. The acids are methanoic, ethanoic, propanoic and butanoic acid. Count the COOH carbon as part of the acid's named total: butanoic acid CH₃CH₂CH₂COOH has four carbons, not three. HCOOH is methanoic acid, with its single carbon inside COOH.
Number the feature rather than the page orientation
For these alkene examples, choose the end giving the C=C the lower position number; the number identifies the first carbon of the double bond. But-1-ene is CH₂=CHCH₂CH₃ and but-2-ene CH₃CH=CHCH₃. They share C₄H₈ but have different double-bond positions. Turning the same drawing around does not change its name or create a third butene.
For the specified alcohols, the number identifies the carbon bearing OH, using the lower available number. Propan-1-ol CH₃CH₂CH₂OH and propan-2-ol CH₃CH(OH)CH₃ both total C₃H₈O; butan-1-ol CH₃CH₂CH₂CH₂OH and butan-2-ol CH₃CH(OH)CH₂CH₃ both total C₄H₁₀O. Complete the remaining H atoms to give ordinary C four and neutral O two bonds. The acid's carboxyl carbon starts the acid chain's numbering.
Pause and explain
Which structural formula is propan-2-ol?
Worked example
Compare but-1-ene with but-2-ene and propan-1-ol with propan-2-ol, stating what the position changes and what stays the same.
Show the worked solution
- But-1-ene has the end C=C in CH₂=CHCH₂CH₃; but-2-ene has the middle C=C in CH₃CH=CHCH₃.
- Both butenes total C₄H₈ but differ structurally.
- Propan-1-ol has OH on an end carbon; propan-2-ol has OH on the middle carbon. Both total C₃H₈O.
Answer Butenes: end versus middle C=C, both C₄H₈. Propanols: end versus middle OH, both C₃H₈O.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Draw and name the two specified unbranched C₄H₈ alkenes with every H and bond.
Give me a hint
Place C=C at carbon 1 or carbon 2, then complete carbon valences.
Compare my reasoning
- But-1-ene has CH₂=CHCH₂CH₃, with its end double bond.
- But-2-ene has CH₃CH=CHCH₃, with its middle double bond.
- Show every H separately; each drawing totals C₄H₈ and gives four bonds at each C.
But-1-ene CH₂=CHCH₂CH₃ and but-2-ene CH₃CH=CHCH₃, both displayed fully and totalling C₄H₈.
Look for these in your work
- Names and double-bond positions match.
- Every atom and bond is drawn with correct totals.
Write and display both propanol and both butanol position variants, naming each.
Give me a hint
Give each OH-bearing carbon only the remaining number of C–H bonds.
Compare my reasoning
- Propan-1-ol CH₃CH₂CH₂OH and propan-2-ol CH₃CH(OH)CH₃ total C₃H₈O.
- Butan-1-ol CH₃CH₂CH₂CH₂OH and butan-2-ol CH₃CH(OH)CH₂CH₃ total C₄H₁₀O.
- Expand each group into all atoms/bonds and verify C four, O two and H one, including the O–H hydrogen.
Propan-1-ol / propan-2-ol: C₃H₈O. Butan-1-ol / butan-2-ol: C₄H₁₀O, with the OH positions and all bonds displayed as in the reference.
Look for these in your work
- All four required position variants are named.
- OH position and adjusted hydrogens agree with each drawing.
A drawing shows CH₃CH₂CH₂COOH but is called propanoic acid, and a rotated but-1-ene drawing is called a third C₄H₈ isomer. Assess both names.
Give me a hint
Count the acid carbon and compare actual connections before renaming.
Compare my reasoning
- CH₃CH₂CH₂COOH contains four carbons including COOH, so it is butanoic acid.
- Rotating the entire but-1-ene drawing preserves its double-bond position relative to the chain end.
- It remains but-1-ene, not a new structural isomer; a connectivity change is needed.
The acid is butanoic acid; whole-diagram rotation leaves but-1-ene unchanged and does not create a new isomer.
Look for these in your work
- The carboxyl carbon is counted.
- Orientation is separated from structural connectivity.
Common mistakes
- Inventing a one-carbon simple alkene.
- Numbering from the end that gives the stated feature a larger position.
- Omitting the COOH carbon from the acid's name count.
- Moving OH without adjusting the carbon-bound hydrogen counts.
What can you explain now?
Name CH₃CH(OH)CH₂CH₃ and give its molecular total.
Compare with the explanation
Butan-2-ol, C₄H₁₀O.
The OH is on carbon 2 of an unbranched four-carbon chain; include its hydrogen in the total.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Use the four expandable family groups: draw a named example before opening its reference, then check position numbers, atom totals and every bond.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.