Haloalkanes Flashcards
What is a haloalkane?
A compound in which a halogen atom has replaced at least one of the hydrogen atoms in an alkane chain.
Is a carbon-halogen bond polar or non polar and why?
Polar, because the halogen atom is more electronegative than carbon.
What species does the electron deficient C atom attract?
Nucleophiles.
What is a nucleophile?
An electron pair donor.
What are examples of nucleophiles?
OH-
NH3
H2O
CN-
What is nucleophilic substitution?
An electron pair donor replaces a halogen atom.
What is hydrolysis?
A chemical reaction involving water/an aqueous solution of a hydroxide ion that causes the breaking of a bond in a molecule.
What reagents/conditions/products are required for nucleophilic substitution of a haloalkane and hydroxide ions?
- aqueous alkali e.g., NaOH
- heat under reflux
- forms an alcohol and a halogen ion
What does heating under reflux involve?
The continuous boiling and condensing of a liquid, allowing prolonged heating and preventing loss by evaporation.
What does the reactivity of a haloalkane depend on?
The strength of the carbon-halogen bond which breaks during the reaction by heterolytic fission.
State the order of reactivity of haloalkanes.
MOST REACTIVE/WEAKEST BOND
- C-I
- C-Br
- C-Cl
- C-F
LEAST REACTIVE/STRONGEST BOND
What reagents/conditions/products are present in measuring the rate of hydrolysis of primary haloalkanes?
- aqueous silver nitrate, AgNO3(aq)
- ethanol solvent and heat(water bath)
- alcohol and silver halide
How do you calculate the rate of hydrolysis?
1/time.
What are the results of the rate of hydrolysis with Cl, Br and I?
Cl- white precipitate, most time, slowest rate
Br- cream precipitate
I- yellow precipitate, least time, fastest rate
Why is the rate of hydrolysis of 1-iodobutane faster than the rate of hydrolysis of 1-chlorobutane?
-the rate of hydrolysis depends upon the strength of the Carbon-Halogen bond
-the C-I bond is weaker than the C-Cl bond
-less energy is needed to break the C-I bond so the rate of hydrolysis is faster
What are CFCs?
Chloro Flouro Carbons.
What were the uses of CFCs?
Refrigerants, aerosol propellants.
Why are CFCs no longer used?
Their use results in the depletion of the ozone layer.
What has replaced CFCs?
HFCs (hydroflourocarbon) and HCFCs (hydrochloroflourocarbons).
What is the ozone layer?
A region of the Earth’s stratosphere that absorbs the Sun’s harmful UV radiation. It contains high concentrations of ozone(O3).
What does UV initially break oxygen molecules into?
Oxygen radicals
O2→2O.
What has happened to the ozone layer?
The use of CFCs has increased the rate of ozone depletion causing a ‘hole’ in the ozone layer.
Show the equation for the equilibrium involving O2 and oxygen radicals. What does the equation represent?
O2 + O⇌O3
The rate of ozone formation is equal to the rate of ozone depletion.
What is the effect of the depletion of ozone in the ozone layer?
Less protection against the Sun’s UV radiation so a rise in skin cancer.
How have CFCs caused the breakdown of ozone?
CFC molecules produce Cl. radicals in the stratosphere by homolytic fission of a C-Cl bond. The processes of radical substitution.
