Module 4: Chapter 15 (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

a species that can donate a pair of electrons

:OH-, H2O: and :NH3

• 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

• 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

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

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

• 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

• 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

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

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

Propagation steps: NO· + O3 -> NO2· + O2 NO2· + O -> NO· + O2 Overall equation: O3 + O -> 2O2