C15 - Haloalkanes Flashcards
What is a haloalkane?
Compounds containing carbon, hydrogen and at least one halogen
How do you name haloalkanes?
1) Prefix added to longest carbon chain
2) Numbered
3) If more than one haloalkane present, then listed in alphabetical order
What can haloalkanes be classified as?
Primary - carbon attached to 1 alkyl group
Secondary - carbon attached to 2 alkyl groups
Tertiary - carbon attached to 3 alkyl groupss
Why is the carbon-halogen bond polar?
Halogen atoms are more electronegative than carbon atoms
Electron pair closed to halogen atom
Therefore, bond is polar
What’s a nucleophile?
Electron pair donor
Examples of nucleophiles
-Hydroxide ions: OH-
-Water molecules: H2O
-Ammonia molecules: NH3
What is nucleophilic substitution?
Reaction where a nucleophile is attracted to an electron-deficient carbon atom, replacing an atom/group of atoms on the carbon atom
What’s hydrolysis?
Reaction with water that breaks a chemical compound into two compounds
H+ and OH- become incorporated into the two compounds
What mechanism is responsible for the hydrolysis?
Nucleophilic substitution
What happens during the hydrolysis of a haloalkane?
1) Nucleophile, OH-, approaches C atom attached to halogen, from opposite side to halogen
2) Direction of attack by OH- minimises repulsion between nucleophile and delta+ carbon atom
3) Lone pair of e- on OH- is attracted and donated to delta+ carbon atom
4) New bond formed between O atom of OH- and C atom
5) Carbon-Halogen bond breaks by heterolytic fission
6) New organic product is alcohol, halide ion also formed
Hydrolysis of haloalkanes conditions and products
Haloalkane + NaOH (aq) —> Alcohol + sodium halide
Heat and reflux
What happens to carbon-halogen bond strengths down the group?
They decrease
Why happens to reactivity of haloalkanes down the group
Increase
How do you measure the rate of hydrolysis?
Hydrolysis of haloalkanes with water
Carry out reaction in the presence of aq silver nitrate and ethanol solvent
Halide ions exact with silver ions to form precipitate of silver halide
Record time taken for precipitate to form
What happens to the rate of hydrolysis down the group?
Increases
What can organohalogen compounds be used for?
Solvents
Dry cleaning solvents
Polymers
Flame retardants
Refrigerants
What is the ozone layer
Layer found at the outer edge of stratosphere, 10-40km above Earth’s surface
What is the importance of the ozone?
Absorbs most of the damaging UV-B radiation for the Sun’s rays
What impacts does UV-B radiation have?
Linked to sunburn and skin cancer
What is the harm in ozone depletion?
More UV-B radiation will reach Earth’s surface
What is ozone?
O3
How is ozone formed?
O2 —> 2O
UV radiation breaks down O2 into O radicals
O2 + O <=> O3
Steady state formed between O2 and O radicals where O3 forms and breaks downs
What’s is a CFC
Chlorofluorocarbons
What is a HCFC
hydrochlorofluorocarbons
Why are CFCs stable
C-X bond strength
What we’re CFCs and HCFCs used before
Refrigerant
Air conditioning units
Aerosol propellants
Why are CFCs harmful?
-CFCs remain stable until they reach the stratosphere
-Then they break down forming chlorine radius,w
-Cl radicals catalyse the breakdown of teh ozone
Why do CFCs take years to reach the stratosphere?
-Strong C-X bonds mean long residence time in troposphere
What happens to CFCs in the stratosphere?
UV radiation breaks C-Cl bond by homolytic fission forming radicals
Photodissociation of CF2Cl2 equation
CF2Cl2 —> CF2Cl (radical) + Cl (radical)
What is photodissociation?
Break down of chemical compound by light
What are the two propagation steps of the breaks down of ozone?
Cl radical + O3 —> ClO radical + O2
ClO radical + O —> Cl radical + O2
What is the overall equation of breakdown of ozone?
O3 + O —> 2O2
Are only CFCs responsible for ozone-depleting reactions?
No, other radicals too
Give another example of a radical responsible for ozone-depleting reactions
NO radical + O3 —> NO2 radical + O2
NO2 radical + O —> NO radical + O2
