Halogen compounds
Cambridge A-Level Chemistry (9701) · Unit 31: Hydroxy compounds (A Level) · 6 flashcards
Halogen compounds is topic 31.1 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 31 — Hydroxy compounds (A Level) . In one line: Methylbenzene reacts with chlorine (Cl₂) and AlCl₃ to form 2-chloromethylbenzene and 4-chloromethylbenzene. The methyl group directs the chlorine to the ortho (position 2) and para (position 4) positions.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 6 flashcards — 1 definition and 5 key concepts — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The possible products when methylbenzene reacts with chlorine in the presence of an AlCl₃ catalyst
Methylbenzene reacts with chlorine (Cl₂) and AlCl₃ to form 2-chloromethylbenzene and 4-chloromethylbenzene. The methyl group directs the chlorine to the ortho (position 2) and para (position 4) positions.
What the Cambridge 9701 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- recall the reactions by which halogenoarenes can be produced: substitution of an arene with Cl₂ or Br₂ in the presence of a catalyst, Al Cl₃ or Al Br₃ to form a halogenoarene, exemplified by benzene to form chlorobenzene and methylbenzene to form 2-chloromethylbenzene and 4-chloromethylbenzene
- explain the difference in reactivity between a halogenoalkane and a halogenoarene as exemplified by chloroethane and chlorobenzene
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Halogen compounds
- › Recall the relative oxidizing strengths of halogens; HCl cannot oxidize iodide, and silver chloride is soluble in aqueous ammonia.
- › For the formation of NaClO, specify that sodium hydroxide must be cold and in aqueous solution.
Describe the reaction conditions and reagents required to produce chlorobenzene from benzene.
Benzene reacts with chlorine (Cl₂) in the presence of a catalyst such as aluminium chloride (AlCl₃). This electrophilic substitution reaction substitutes a hydrogen atom on the benzene ring with a chlorine atom, forming chlorobenzene and HCl.
What are the possible products when methylbenzene reacts with chlorine in the presence of an AlCl₃ catalyst?
Methylbenzene reacts with chlorine (Cl₂) and AlCl₃ to form 2-chloromethylbenzene and 4-chloromethylbenzene. The methyl group directs the chlorine to the ortho (position 2) and para (position 4) positions.
Explain why halogenoarenes are significantly less reactive than halogenoalkanes in nucleophilic substitution reactions.
The carbon-halogen bond in halogenoarenes is stronger due to the delocalization of the lone pair of electrons on the halogen into the π-system of the benzene ring, giving it partial double bond character. This increased bond strength makes it harder to break compared to the C-X bond in halogenoalkanes.
Describe one factor that affects the rate of nucleophilic substitution in halogenoalkanes, but is not relevant in halogenoarenes.
Steric hindrance around the carbon atom bonded to the halogen. Bulky alkyl groups in halogenoalkanes can hinder the approach of the nucleophile, slowing down the reaction. This is less relevant in halogenoarenes as the benzene ring provides a different type of steric environment.
How does the stability of the carbocation intermediate affect the reactivity of halogenoalkanes vs. halogenoarenes?
Halogenoalkanes can form relatively stable carbocations during SN1 reactions. However, the formation of a carbocation from a halogenoarene would require breaking the aromatic system, which is energetically unfavorable and does not occur under normal conditions.
Outline the mechanism for the reaction between benzene and chlorine in the presence of AlCl₃, forming chlorobenzene.
The reaction proceeds via electrophilic substitution. AlCl₃ acts as a Lewis acid catalyst, polarizing the Cl-Cl bond. The benzene ring acts as a nucleophile, attacking the partially positive chlorine. This forms a carbocation intermediate, which then loses a proton to regenerate the aromatic system, forming chlorobenzene and HCl.
More Chemistry flashcards
Browse every 9701 flashcard topic by syllabus area.
All Chemistry FlashcardsKey terms covered in this Halogen compounds deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Halogen compounds deck
Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.
Study Mode
Rate each card Hard, Okay, or Easy after flipping.