Name the mechanism for the reaction of 1-bromobutane with aqueous potassium hydroxide.
[1 mark]
Total for this question: 1
Chemistry
Halogenoalkanes
AQA 3.3.3
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
Board and spec code confirmed against AQA 7405 · registry checked 2026-07-11How this checking works
The topic on one screen
- Nucleophilic substitution with OH- (aqueous, warm), CN- (aqueous ethanol, warm) and excess NH3 (ethanol, sealed tube).
- Same halogenoalkane, different conditions: aqueous KOH → substitution (alcohol); hot ethanolic KOH → elimination (alkene).
- Rate of hydrolysis follows bond enthalpy: C-I < C-Br < C-Cl, so iodoalkanes react fastest — electronegativity is the wrong argument.
- Elimination needs a hydrogen on the carbon NEXT TO the C-X carbon; unsymmetrical halogenoalkanes can give more than one alkene.
- CFCs and ozone: Cl radicals catalyse ozone breakdown — two propagation steps, Cl* regenerated.
Where students actually lose marks
The solvent for the nitrile step — KCN in AQUEOUS ETHANOL — keeps being ignored, even though it has been asked repeatedly. Water alone favours substitution by OH-; name the mixed solvent.
June 2023 Paper 2 examiner report (Q04.3)
Mechanism marks die on sloppy curly arrows: arrows must start at the lone pair or bond and land exactly where the electrons go, and the intermediate/transition structure has to be drawn correctly.
June 2022 Paper 2 examiner report (Q01.8)
When a synthesis route needs UV light for a radical step, examiners report it 'often incorrect or omitted' — conditions are marks, not decoration.
June 2022 Paper 2 examiner report (Q10.3)
Try it — exam-style
Easy
ORIGINAL
Medium
ORIGINAL
State the reagent and conditions needed to convert 2-bromopropane into propene, and name the mechanism.
[3 marks]
Total for this question: 3
Hard
ORIGINAL · after June 2023 Paper 2 Q04.3
A student converts 1-bromopropane into butanenitrile using potassium cyanide. Explain why the reaction is carried out in aqueous ethanol rather than water alone.
[2 marks]
Total for this question: 2
Hard
ORIGINAL
1-iodobutane is hydrolysed by warm water faster than 1-chlorobutane. Explain why, and state why an electronegativity argument gives the wrong prediction.
[3 marks]
Total for this question: 3
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
Get the printable question packbrowser print viewDrill it properly
Draw the mechanism — hydroxide substitution
Curly arrows with mark-scheme feedback, like the exam.
Draw the mechanism — elimination
The substitution/elimination fork, drawn step by step.
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Chemistry flashcards
Reagents and conditions cards for every 3.3.3 reaction.
Stuck on halogenoalkanes?
Substitution vs elimination conditions trip up nearly every student I meet — one lesson sorts the fork for good. Free intro call, then a free first lesson.