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Halogenoalkanes
This topic links polar carbon-halogen bonds to reaction pathways and atmospheric effects.
11
Objectives
55
Flashcards
55
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
polar carbon-halogen bondnucleophilic substitutionNucleophilic substitutionHydroxide ion (OH-)carbon-halogen bond enthalpyreaction ratehydrolysishydroxide ionnucleophilehalogenoalkanesEliminationozone layer
Exam tips
- Understanding Polar Bonds in Halogenoalkanes: Identify the electronegativity difference between carbon and halogen atoms to explain the polarity of carbon-halogen bonds in halogenoalkanes.
- Understand Nucleophilic Substitution Mechanisms: Familiarize yourself with the mechanisms of nucleophilic substitution involving OH-, CN-, and NH3. Practice drawing the reaction pathways and identifying the nucleophile and leaving group.
Common mistakes
- Misunderstanding Polar Bonds in Halogenoalkanes: Halogenoalkanes contain polar bonds due to the difference in electronegativity between carbon and halogen atoms. The halogen atom attracts the bonding electrons more strongly than the carbon atom, creating a dipole moment. This polarity leads to the halogenoalkanes having distinct physical properties, such as higher boiling points compared to non-polar compounds.
- Understanding Nucleophilic Substitution: To clarify, remember that nucleophiles are electron-rich species that donate a pair of electrons to form a bond, while electrophiles are electron-deficient species that accept electron pairs. For example, in the reaction of a halogenoalkane with OH-, the hydroxide ion (OH-) acts as the nucleophile, attacking the carbon atom bonded to the halogen, which is the electrophile due to its partial positive charge.
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