Chemistry AS ES CI 13.1
- Created by: A.B.
- Created on: 19-02-14 12:07
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- ES Halogenoalkanes CI 13.1
- Naming Halogenalkanes
- The alkane chain is prefixed with the name of the halogen.
- Alphabetical order
- Number indicates the position of each
- The alkane chain is prefixed with the name of the halogen.
- Physical Properties of Halogenoalkanes
- The boiling points increase with a heavier halogen atom (R-> I) or with increasing number of halogen atoms (CCL4 > CH2Cl2)
- As the halogen introduced is larger or the number of halogen atoms increases, the overall number of electrons increases. Increases the number of ID - ID bonds, more energy needed to break.
- Bond Enthalpies and Reactivity of Halogenoalkanes
- The C-Hal bond becomes weaker as the size of the halogen atom increases. This makes the bond easier to break and the compounds more reactive.
- Although the C - F bond is most polar, fluoroalkanes are relatively unreactive.
- Bond STRENGTH rather than POLARITY has greatest effect on the reactivity of halogenoalkanes.
- Fluoro - compounds are very unreactive
- Chloro - compounds are reasonably stable in the troposphere and can react to produce chlorine radicals that deplete ozone.
- Bromo - and iodo - compounds are reactive and so are useful as intermediates in chemical synthesis.
- Bond STRENGTH rather than POLARITY has greatest effect on the reactivity of halogenoalkanes.
- Reactions of Halogenoalkanes
- Homolytic fission
- forming radicals
- gas phase with high temperatures, or the presence of UV radiation
- Heterolytic fission
- dissolved in a polar solvent such as an ethanol/water mixture
- The C - H bond breaks to give ions. Ig the polar C-Hal bond is broken completely a negative halide ion, leaving a carbocation
- Substitution reactions
- The C - Hal bond breaks and the halogen is replaced by another functional group.
- Since the halogen is replaces by a nucleophile these reactions are called nucleophilic substitution reactions.
- The C - Hal bond breaks and the halogen is replaced by another functional group.
- Homolytic fission
- Preparation of Halogenoalkanes
- Stages in purification of the chloroalkane:
- 1. The upper layer containing the chloroalkane is run off into a clear beaker
- 2. the chloroalkane is shaken with a solution of sodium hydrogen carbonate to remove any acidic impurities
- 3. The chloroalkane layer is run off for a second time
- 4. Andhydrous sodium sulfate (a drying agent ) is added to remove any water
- 5. The chloroalkane is purified by distillation
- 4. Andhydrous sodium sulfate (a drying agent ) is added to remove any water
- 3. The chloroalkane layer is run off for a second time
- 2. the chloroalkane is shaken with a solution of sodium hydrogen carbonate to remove any acidic impurities
- 1. The upper layer containing the chloroalkane is run off into a clear beaker
- Stages in purification of the chloroalkane:
- Naming Halogenalkanes
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