Butan-1-ol is an alcohol that can be produced by fermentation. Describe the structure of butan-1-ol and explain how it differs from a halogenoalkane, giving one example of a halogenoalkane that could be produced from butan-1-ol.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Butan-1-ol belongs to the alcohol homologous series and has the molecular formula C₄H₉OH.
Model answer (5 marks)
Butan‑1‑ol has a straight‑chain of four carbon atoms with a hydroxyl group attached to the first carbon.
The –OH group is bonded to the terminal carbon (C‑1) of the chain.
In a halogenoalkane the –OH group is replaced by a halogen atom (Cl, Br, I, F) or a halogen substitutes a hydrogen atom on the chain.
An example that could be made from butan‑1‑ol is 1‑chlorobutane (C₄H₉Cl).
Thus the –OH group in butan‑1‑ol is replaced by a halogen atom to give the halogenoalkane.
The –OH group is bonded to the terminal carbon (C‑1) of the chain.
In a halogenoalkane the –OH group is replaced by a halogen atom (Cl, Br, I, F) or a halogen substitutes a hydrogen atom on the chain.
An example that could be made from butan‑1‑ol is 1‑chlorobutane (C₄H₉Cl).
Thus the –OH group in butan‑1‑ol is replaced by a halogen atom to give the halogenoalkane.
Examiner tips
- Use the exact wording ‘hydroxyl group’ and ‘halogenoalkane’. Show the –OH on C‑1 and the halogen on C‑1 in the example. Give a correct IUPAC name (1‑chlorobutane) or formula (C₄H₉Cl).
Common mistakes
- Writing the –OH on a middle carbon instead of C‑1. Using a non‑halogenated alkane as the example. Omitting the halogen replacement step in the explanation.
Mark scheme (5 marks)
- Butan-1-ol contains a hydroxyl (–OH) group
- The –OH group is attached to the first carbon atom in the chain
- A halogenoalkane contains a halogen atom in place of the hydroxyl group (or in place of a hydrogen atom)
- A correct named or formulaic example of a halogenoalkane that could be produced from butan-1-ol (e.g. 1-chlorobutane / C₄H₉Cl)
- The –OH group in butan-1-ol is replaced by a halogen atom to form the halogenoalkane
Key terms in this question
Related
- All WJEC A-Level Chemistry (Wales) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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