Chapter 15 - Chemistry of Haloalkanes Flashcards
General formula of Haloalkanes?
CnH2n+1X
Polarity of haloalkanes?
Halogen atoms are more electronegative than carbon. The C-X bond polarity decreases from F –> I .
Polarity of the C-X bond attracts nucleophiles to the Carbon atom with partial positive charge.
What is a nucleophile?
A nucleophile is an atom or group of atoms that donates an electron pair to an electron-deficient centre.
- Electron donator
- Usually electron rich and may be a negative ion, with a lone pair, or a molecule containing an atom with a partial negative charge
What is nucleophilic substitution?
Nucleophile replaces the halogen in the haloalkane, which is lost as a halide ion.
What are the nucleophilic substitution steps?
- The OH- ion acts as a nucleophile, donating an electron to the partially positive carbon atom
- A new bond forms between the oxygen atom of the OH- ion and the carbon atom
- The carbon-halogen bond breaks by heterolytic fission
- organic product formed is an alcohol + halide ion is formed
Hydrolysis of Haloalkane?
Alcohol + h+ion + halide ion formed
Halide ions react with silver ions to form what?
Forms silver halide precipitate.
- The rates of hydrolysis of different carbon-halogen bonds can be measured by measuring the time for silver halide precipitate to form
- The lower the bond enthalpy, the faster the haloalkane reacts
- I reacts faster than Br and that reacts faster than Cl
Benefits of the Ozone layer?
Helps filter out harmful UV radiation which is harmful to us which can cause skin cancer, cataracts and damage to crops.
CFC molecules in the presence of UV radiation?
C-Cl bonds are broken by homolytic fission to form radicals.
CFC molecule = CCl3F
Breakdown = CCl3F –> .CCl2F + Cl.
The breakdown of ozone catalysed by Cl. radicals.
The two Propagation steps?
- Cl. + O3 –> ClO. + O2
- ClO. + O –> Cl. + O2
overall: O3 + O –> O2
