Halogen compounds — AS & A Level Chemistry (9701) questions by topic
Nucleophilic substitution and elimination mechanisms anchor this topic: comparing reaction rates of chlorobutane against iodobutane, deciding solvent and reaction type when bromoethane forms ethene, and naming nitriles produced from halogenoalkanes systematically.
Deduce, identify, state, explain and express dominate 37 questions from 2023 to 2025 papers, worth 1 to 15 marks, where naming slips or a missing reflux condition can cost marks even when the mechanism is right. Instant marking after each mechanism or naming answer flags a non-systematic name such as propionitrile, or a missing 'e' in propanenitrile, before the same slip repeats in a later organic question.
What examiners look for
- A recurring criticism is giving non-systematic names such as propionitrile or ethyl cyanide, or omitting the 'e' in propanenitrile.
- Examiners note candidates stating acidic conditions but omitting heat under reflux, which loses a condition mark.
- Reports flag failing to test which elimination products give chiral versus non-chiral dibromides on reaction with Br2 as a common gap.
- Strong answers appreciated that the essential condition was heat under reflux, ensuring complete oxidation to the carboxylic acid.
- Candidates who identified that KCN reacts with bromoethane to form propanenitrile, later hydrolysed by dilute HCl to propanoic acid, reached the correct answer D.
May–June 2025, Paper 11
Two reactions are described. 1 2-bromo-2-methylbutane heated with NaOH(aq) 2 2-chloro-2-methylbutane heated with NaOH(aq) In both reactions, the conditions are the same and…
Answer this question and get it marked →May–June 2025, Paper 12
Which statement about the mechanism of an SN1 reaction of a halogenoalkane is correct? A A nucleophile is substituted by an electrophile. B One intermediate is formed from two…
Answer this question and get it marked →Four reagents are listed. 1 aqueous KCl 2 dilute HCl 3 liquid SOCl2 4 solid PCl5 Which reagents, when added to ethanol, will rapidly produce a gas that turns blue litmus red? A 1…
Answer this question and get it marked →Four drops of 1-chlorobutane, 1-bromobutane and 1-iodobutane are put separately into three test-tubes containing 1.0 cm^3 of aqueous silver nitrate at 60 °C. In each case, a…
Answer this question and get it marked →May–June 2025, Paper 13
The reaction shown can be used to lengthen a carbon chain. CH3CH2CH2Br + CN^- → CH3CH2CH2CN + Br^- Which row shows the correct reagent and conditions for this reaction? A KCN,…
Answer this question and get it marked →May–June 2025, Paper 14
Which reagent would react with 1-bromopropane to give the highest yield of propene? A ammonia B aqueous potassium hydroxide C potassium cyanide D ethanolic sodium hydroxide
Answer this question and get it marked →May–June 2024, Paper 11
Q is either a primary or a tertiary halogenoalkane. Q undergoes hydrolysis with aqueous sodium hydroxide. The first step in the mechanism of this reaction involves two species…
Answer this question and get it marked →2-bromopropane is converted to 1,2-dibromopropane in a pathway involving two reactions: 2-bromopropane - (reaction 1) - compound X - (reaction 2) - 1,2-dibromopropane. What are…
Answer this question and get it marked →May–June 2024, Paper 12
Aqueous NaOH reacts with 1-bromopropane to give propan-1-ol. What should be included in a diagram of the first step in the mechanism? A a curly arrow from a lone pair on the OH^-…
Answer this question and get it marked →1-bromopropane reacts with hot ethanolic NaOH. What is the molecular formula of the product in this reaction? A C3H6 B C3H8 C C3H7O D C3H8O
Answer this question and get it marked →May–June 2024, Paper 13
What is involved in the mechanism of the reaction between aqueous NaOH and 1-bromobutane? A attack by a nucleophile on a carbon atom with a partial positive charge B heterolytic…
Answer this question and get it marked →When heated with KOH dissolved in ethanol, halogenoalkanes can undergo an elimination reaction to form alkenes. What are the possible elimination products when 2-bromobutane is…
Answer this question and get it marked →Chloroethane can be used to make sodium propanoate. chloroethane - intermediate Q - sodium propanoate Intermediate Q is hydrolysed with boiling aqueous NaOH to give sodium…
Answer this question and get it marked →October–November 2024, Paper 11
When X is added to NaOH(aq) and heated under reflux, pentan-2-ol is made. Which organic product is made when X is heated with a solution of KCN dissolved in ethanol? X is…
Answer this question and get it marked →1-chlorobutane and 1-iodobutane both react with aqueous sodium hydroxide by a nucleophilic substitution mechanism. Which reaction has the greatest rate under the same conditions…
Answer this question and get it marked →October–November 2024, Paper 12
What is true of every nucleophile? A It attacks a double bond. B It donates a lone pair of electrons. C It is a single atom. D It is negatively charged.
Answer this question and get it marked →The diagram shows a synthetic route to produce 1-methylcyclohexanol. 1-methylcyclohex-1-ene reacts with HBr to give product X (1-bromo-1-methylcyclohexane), and X is then heated…
Answer this question and get it marked →X and Y are the reagents required to convert 1-bromopropane into butanoic acid. 1-bromopropane (CH₃CH₂CH₂Br) reacts with reagent X to give butanenitrile (CH₃CH₂CH₂CN), which then…
Answer this question and get it marked →The table shows three sets of reagents and reaction conditions. reagents reaction conditions --- --- --- 1 CH₂C(CH₃)CH₃ and HCl(g) room temperature 2 CH₃C(CH₃)(OH)CH₃ and SOCl₂…
Answer this question and get it marked →October–November 2024, Paper 13
When X is added to NaOH(aq) and heated under reflux, pentan-2-ol is made. Which organic product is made when X is heated with a solution of KCN dissolved in ethanol? X is…
Answer this question and get it marked →1-chlorobutane and 1-iodobutane both react with aqueous sodium hydroxide by a nucleophilic substitution mechanism. Which reaction has the greatest rate under the same conditions…
Answer this question and get it marked →February–March 2023, Paper 12
Which reagents and conditions would result in the formation of butanenitrile, CH3CH2CH2CN? A 1-bromobutane heated under pressure with ammonia in ethanol B 1-bromopropane heated…
Answer this question and get it marked →Compound X, C7H13Br, reacts with hot alcoholic NaOH to produce two compounds, Y and Z. On reaction with Br2, Y gives a product, C7H12Br2, which exists as a mixture of four optical…
Answer this question and get it marked →Which compound reacts most rapidly with aqueous silver nitrate by an SN1 mechanism? A 1-chloromethylpropane B 2-chloromethylpropane C 1-iodomethylpropane D 2-iodomethylpropane
Answer this question and get it marked →February–March 2023, Paper 22
Fig. 4.1 shows some reactions of compound D, 2-bromobutane. State the reagent and conditions used to form E in reaction 1.
Answer this question and get it marked →May–June 2023, Paper 11
Which row describes the solvent used and type of reaction occurring when bromoethane reacts with NaOH to form ethene? solvent type of reaction --- --- --- A ethanol elimination B…
Answer this question and get it marked →Which statement describes what happens when 2-chloro-2-methylpropane is warmed with NaOH(aq)? A This secondary halogenoalkane reacts by a mixture of an SN1 and an SN2 mechanism. B…
Answer this question and get it marked →May–June 2023, Paper 12
When bromoethane reacts with hot ethanolic sodium hydroxide a colourless gas is formed. This gas decolourises aqueous bromine. What is the colourless gas? A 1,2-dibromoethane B…
Answer this question and get it marked →Halogenoalkanes react with hot ethanolic potassium cyanide. The reaction mechanism is either SN1 or SN2. Which statement is correct? A All secondary halogenoalkanes react by the…
Answer this question and get it marked →May–June 2023, Paper 13
Structural isomerism and stereoisomerism should be considered when answering this question. 2-bromopentane is heated with an excess of ethanolic sodium hydroxide. How many…
Answer this question and get it marked →Which type of reaction happens during the hydrolysis of 2-bromopropane? A electrophilic addition B free radical substitution C nucleophilic addition D nucleophilic substitution
Answer this question and get it marked →May–June 2023, Paper 22
Fig. 3.1 describes a sequence of reactions used to produce a food additive, compound Y, from CH3CH2Cl. Step 1: CH3CH2Cl - X (CH3CH2CN). Step 2: X + dilute acid - CH3CH2COOH. Step…
Answer this question and get it marked →May–June 2023, Paper 42
Describe the difference in reactivity between chloroethane and chlorobenzene with OH⁻(aq). Explain your answer.
Answer this question and get it marked →October–November 2023, Paper 11
1,1-dichloropropane reacts with aqueous sodium hydroxide in a series of steps to give propanal: CH3CH2CHCl2 reacts with NaOH(aq) to give CH3CH2CHO. Which term describes the first…
Answer this question and get it marked →October–November 2023, Paper 12
Which row shows the correct name and classification of the halogenoalkane CH3(CH2)2CBr(CH3)CH2CH3? A: 3-bromo-3-methylhexane, secondary. B: 3-bromo-3-methylhexane, tertiary. C:…
Answer this question and get it marked →October–November 2023, Paper 13
1,1-dichloropropane reacts with aqueous sodium hydroxide in a series of steps to give propanal. CH3CH2CHCl2 --NaOH(aq)-- CH3CH2CHO Which term describes the first step of this…
Answer this question and get it marked →Propanoic acid can be made from bromoethane using a two-stage synthesis. Which pair of reagents is most suitable? reagent for stage 1 reagent for stage 2 --- --- --- A hydrogen…
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