Haloalkanes
- Created by: Siana
- Created on: 11-02-14 19:33
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- Haloalkanes
- What is a Haloalkane?
- Haloalkanes have an alkane skeleton with one or more halogen
- Fluorine, Chlorine, Bromine, or Iodine
- Replaces H atoms
- General Formula
-
CnH2n+1X
- X is the Hydrogen
- Shortened to R--X
-
CnH2n+1X
- Bond Polarity
- Haloalkanes have a polar bond ( Co+-- Xo-)
- As you go down the group of halogens they become less polar.
- Electronegativity decreases
- Physical Properties
- Solubility
- Not soluble in water
- Intermolecular forces
- Dipole-Dipole
- V-D-W's
- Mix with hydrocarbons
- Boiling Point
- B.pt increases with increased chain length
- B.pt increases as we go down the halogen group
- Solubility
- NUCLEOPHILIC SUBSTITUTION
- These are reactions in which the bond between the carbon atom and the halogen atom breaks by HETEROLYTIC FISSION
- When the bond breaks; one atom gets a lone pair of electrons, the other gets none.
- Ions are formed
- Rates of nucleophilic substitution
- Depends on the halogen
- F-C is the strongest - fluoroalkanes are lest reactive
- Longer bonds = weaker bonds
- Depends on the nature of the halogenoalkane
- Order of reactivity: 3'>2'>1'
- Depends on the halogen
- HYDROLYSIS using OH-
- Hydroxide ion acting as NUCLEOPHILE
- Conditions
- Aqueos ethanol (solvent)
- KOH or NaOH (aq)
- Room temperature
- ELIMINATION using OH-
- OH- acting as NUCLEOPHILE
- Conditions
- Dry ethanol (solvent)
- Heat
- ELIMINATION REACTIONS
- Remove H and halogen (e.g. Br) from adjacent cations in a halogenoalkane (alkanes)
- Eliminated HBr is ACID
- achieved using a strong base
- Hot, conc NaOH (ethanol) suitable
- Converts HX to salt (NaBr) and water
- FREE RADICAL SUBSTITUTION
- INITIATION
- U.V light breaks covalent bond (Cl--Cl) by homolytic fission producing 2 free radicals
- PROPEGATION
- A whole alkane or haloalkane reacts with a free radical to form another free radical - carrying on the reaction
- TERMINATION
- Two radicals react to form a whole alkane or haloalkane
- CFC's and the OZONE layer
- Ozone layer made up of O3
- U.V. light breaks down CFC's to make free radicals
- Cl. + O3 --> ClO. + O2
- ClO. + O3 --> 2O2 + Cl.
- Chlorine atoms catalyse the decomposition of ozone and contribute to holes in the ozone layer
- Legislation to ban use of CFC's by chemists - developed chlorine-free compounds
- Chloroalkanes/ chlorofluoro-alkanes can be used as solvents
- INITIATION
- What is a Haloalkane?
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