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Halogenoalkanes
This topic links polar carbon-halogen bonds to reaction pathways and atmospheric effects.
11
Objectives
10
Flashcards
10
Questions
90 min
Study time
AqaA LevelChemistryOrganic chemistry
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Syllabus checklist
What you need to know
11 objective pages available
Nucleophilic substitution4 objectives
- Explain why halogenoalkanes contain polar bonds.
- Outline nucleophilic substitution mechanisms with OH-, CN- and NH3.
- Explain how carbon-halogen bond enthalpy affects reaction rate.
- Use test-tube hydrolysis evidence to compare reaction rates.
Elimination3 objectives
- Explain the role of hydroxide ions as nucleophile and base.
- Outline elimination mechanisms for halogenoalkanes.
- Compare substitution and elimination conditions.
Ozone depletion4 objectives
- Explain why ozone in the upper atmosphere is beneficial.
- Explain how chlorine radicals are formed from CFCs.
- Use equations to show chlorine radical catalysis of ozone decomposition.
- Explain why scientific evidence led to restrictions on CFCs.
Key terms
PolarityNucleophileLeaving groupHydrolysisBaseE2 mechanismDehydrohalogenationElimination ReactionSubstitution ReactionOzone LayerUltraviolet (UV) RadiationOzone depletion
Exam tips
- Use diagrams to illustrate mechanisms: When explaining nucleophilic substitution, use diagrams to show the movement of electrons and the transition state.
- Use clear mechanisms in your answers: When describing nucleophilic substitution mechanisms, use clear diagrams to illustrate the steps involved.
Common mistakes
- Confusing bond polarity with bond strength: While bond polarity affects reactivity, bond strength also depends on other factors such as atomic size and bond length.
- Confusing SN1 and SN2 mechanisms: Remember that SN1 involves a two-step mechanism with a carbocation intermediate, while SN2 is a one-step process with a direct attack by the nucleophile.
Practice preview
- Which of the following statements correctly explains why halogenoalkanes contain polar bonds?
- Explain the significance of the polarity in halogenoalkanes when considering their reactivity.
- A student is investigating the reactivity of different halogenoalkanes in nucleophilic substitution reactions. They hypothesize that the bond polarity affects the reaction rate. Describe how the student could test this hypothesis.
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