Propan-1-ol (CH₃CH₂CH₂OH) and 1-chloropropane (CH₃CH₂CH₂Cl) belong to different homologous series. Describe the similarities and differences between the structures of these two compounds, and explain how 1-chloropropane can be converted back to propan-1-ol.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Propan-1-ol is an alcohol used as a solvent in industry. 1-Chloropropane is a halogenoalkane that can be made from propan-1-ol.
Model answer (5 marks)
Both compounds have the same three‑carbon chain (CH₃CH₂CH₂–). Propan‑1‑ol has a hydroxyl –OH group attached to the terminal carbon, whereas 1‑chloropropane has a chlorine atom (–Cl) in the same position. Thus they share the carbon skeleton but differ in the functional group: alcohol versus halogenoalkane.
To convert 1‑chloropropane back to propan‑1‑ol, treat it with aqueous sodium hydroxide (NaOH). The –Cl is displaced by the –OH group in a nucleophilic substitution (Sₙ2) reaction, giving propan‑1‑ol and sodium chloride.
To convert 1‑chloropropane back to propan‑1‑ol, treat it with aqueous sodium hydroxide (NaOH). The –Cl is displaced by the –OH group in a nucleophilic substitution (Sₙ2) reaction, giving propan‑1‑ol and sodium chloride.
Examiner tips
- Mention the common carbon chain and the differing functional groups; state the reaction type (Sₙ2) and reagents (NaOH, aqueous); keep the answer concise and use correct terminology –OH, –Cl, halogenoalkane, alcohol.
Common mistakes
- Confusing the position of the –OH/–Cl (placing them on the wrong carbon); using the wrong reagent (e.g., NaCl instead of NaOH); failing to note that the reaction is a substitution, not addition.
Mark scheme (5 marks)
- Both compounds contain the same carbon chain / both have three carbon atoms / same carbon skeleton
- Propan-1-ol contains an –OH (hydroxyl) functional group whereas 1-chloropropane contains a halogen (chlorine / –Cl) functional group
- They belong to different homologous series — propan-1-ol is an alcohol and 1-chloropropane is a halogenoalkane
- React 1-chloropropane with sodium hydroxide (NaOH) / aqueous alkali
- The –Cl is replaced by –OH / the chlorine is substituted by a hydroxyl group to form propan-1-ol
Key terms in this question
Related
- All Eduqas A-Level Chemistry revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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