Flashcards in Module 4: Chapter 15 (Haloalkanes) Deck (12)
What are haloalkanes?
- 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
What is a nucleophile?
a species that can donate a pair of electrons
What are some common nucleophiles?
:OH-, H2O: and :NH3
Describe the reactivity of haloalkanes?
- 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
Describe the hydrolysis of haloalkanes?
- 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
- Reactants = aqueous sodium hydroxide and haloalkane
- heat under reflux
What are organhalogen compounds?
Molecules that contain at least one halogen atom joined to a carbon chain
What are the uses of organhalogens?
solvents for cleaning (CHCl3)
dry cleaning solvents (C2HCl2)
making polymers (C2F4)
flame retardants (CF3Br)
What is the ozone (O3) layer?
- 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
Describe the ozone as a steady state?
- 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
What is happening to the ozone layer?
Human activity, especially the production and use of CFC’s has upset this delicate equilibrium.
- CFCs have a long residency time in the atmosphere
What is the photodissociation of CF2Cl2?
Initiation: CF2Cl2 -> CF2Cl· + Cl·
- UV radiation supplies enough energy to break carbon-halogen bonds by homolytic fission forming radicals
Cl· + O3 -> ClO· + O2
ClO· + O -> Cl· + O2
O3 + O -> 2O2