Haloalkanes Flashcards
What is a haloalkane?
A compound containing carbon, hydrogen and at least one halogen
Why is the carbon-halogen bond polar?
Halogen atom more electronegative than the carbon atom
Uneven distribution of electrons, with electrons closer to the halogen
Separation of charge= polarity
Define, fully, a nucelophile
An atom or group of atoms which are attracted to an electron deficient species (carbon atom) where it donates an electron pair to form a new covalent bond
Give 3 examples of a nucleophile
Hydroxide ions
Water molecules
Ammonia molecules
What is nucleophilic substitution?
When haloalkane reacts with a nucleophile, the nucleophile replaces the halogen atom in a substitution reaction. A new compound is formed with a different functional group.
What is hydrolysis?
A chemical reaction involving water or aqueous solution of a hydroxide that causes the breaking of a bond within a molecule.
Explain the 6 basic steps of nucleophilic substitution
1) Nucelophile approaches carbon atom attached to the halogen on the opposite side to the halogen
2) The direction of attack by OH- ion minimises repulsion between the halogen and the OH- ion
3) A lone pair of electrons on the hydroxide ion is attracted to and donated to the carbon atom
4) A new bond is formed between the oxygen and the carbon atom
5) Carbon-Halogen bond breaks by heterolytic fission
6) New organic product is an alcohol. Halide ion formed on the side.
How are haloalkanes converted into alcohols?
Sodium Hydroxide
Heated under reflux
What does the rate of hydrolysis depend on?
Strength of carbon-halogen bond in haloalkane
Which carbon-halogen bond is the most reactive? Why?
Carbon-Iodine, the bond enthalpy is the lowest, and so it is the weakest bond and requires the least energy to overcome.
Briefly explain the experiment that occurs to measure rate of hydrolysis of haloalkanes
Add aqueous silver nitrate to the solution of haloalkane
As reaction occurs the silver and halogen ions will combine to form precipitate in form Ag(+)+ X(-)= AgX(s)
Nucleophile in reaction is water
Carry out in presence of ethanol solvent to ensure one mixture forms not with separated layers
Give six uses of organohalogen compounds
Pesticides Dry Cleaning Making polymers Fire retardants Refrigerants General Solvents
What is the role of the chemical ozone?
To absorb most of the biologically damaging ultraviolet radiation
What are the three risks of UV-B radiation to humans?
Skin Cancer
Increased genetic disorders
Eye damage
What does it mean for ozone to be in a steady state?
The formation of ozone is occurring at the same rate ozone is being broken down
Give 3 uses of CFC’s
Refrigerants
Air conditioning units
Aerosol Propellers
Why are CFCs stable?
Strength of carbon-halogen bonds within the molecules
Where do CFCs remain stable until? Then what happens?
Stratosphere
CFCs break down forming chlorine radicals, catalysing the breakdown of the ozone layer
Why are there concerns CFCs are continuing to cause damage?
Not every country has banned them
Longevity in the troposphere
What does UV radiation do to CFCs?
Provides sufficient energy to break a carbon-halogen bond in CFCs by homolytic fission to form radicals
What is photodissociation?
Radiation initiating the breakdown of a compound
Which other radical catalyses the breakdown of ozone?
Nitrogen Oxide
Where is Nitrogen Oxide formed?
Naturally in lightning strikes
Aircraft travel
