Module 4: Chapter 15 (Haloalkanes)

Question 1

What are haloalkanes?

Answer 1

• haloalkanes are compounds with one or more halogen atoms attached to a hydrocarbon chain
• they are useful
• the halogen causes the relatively unreactive carbon chain to become more reactive

Question 2

What is a nucleophile?

Answer 2

a species that can donate a pair of electrons

Question 3

What are some common nucleophiles?

Answer 3

:OH-, H2O: and :NH3

Question 4

Describe the reactivity of haloalkanes?

Answer 4

• halogen atoms are more electronegative than carbon atoms, the carbon-halogen bond is polar
• the partial positive carbon dipole attracts nucleophiles
• a dative covalent bond is formed
• nucleophile replaces/substitutes the halogen
• the mechanism is nucleophilic substitution

Question 5

Describe the hydrolysis of haloalkanes?

Answer 5

• Reaction in which water/OH-(aq) causes the breaking of a bond in a molecule
• Haloalkane hydrolysis results in a halogen atom being replaced by a hydroxyl group (alcohol formed)
• this is nucleophilic substitution

Conditions:

• Reactants = aqueous sodium hydroxide and haloalkane
• heat under reflux

Question 6

What are organhalogen compounds?

Answer 6

Molecules that contain at least one halogen atom joined to a carbon chain

Question 7

What are the uses of organhalogens?

Answer 7

solvents for cleaning (CHCl3)
dry cleaning solvents (C2HCl2)
making polymers (C2F4)
flame retardants (CF3Br)
refrigerants (F2CCl2)

Question 8

What is the ozone (O3) layer?

Answer 8

• ozone absorbs the biologically damaging UV-B from the Sun
• exposure to UVB causes sun burn and long term effects such as skin care and genetic damage
• located at the top of the stratosphere

Question 9

Describe the ozone as a steady state?

Answer 9

• O2 molecules in the atmosphere absorb UV radiation. The bonds in oxygen molecules break homolytically and produce radicals (O2 -> 2O)
• These radicals are a highly reactive species that contains a single unpaired electron
• Oxygen radical combines with an O2 molecule to make ozone O3
• Ozone absorbs UV radiation and breaks back into oxygen molecules and oxygen radicals
• As these 2 processes happen at the same rate a steady state is created

Question 10

What is happening to the ozone layer?

Answer 10

Human activity, especially the production and use of CFC’s has upset this delicate equilibrium.
- CFCs have a long residency time in the atmosphere

Question 11

What is the photodissociation of CF2Cl2?

Answer 11

Initiation: CF2Cl2 -> CF2Cl· + Cl·
- UV radiation supplies enough energy to break carbon-halogen bonds by homolytic fission forming radicals

Propagation:
Cl· + O3 -> ClO· + O2
ClO· + O -> Cl· + O2

Overall equation:
O3 + O -> 2O2

Question 12

What is the propagation steps for nitrogen oxides?

Answer 12

Propagation steps:
NO· + O3 -> NO2· + O2
NO2· + O -> NO· + O2

Overall equation:
O3 + O -> 2O2