Chapter 15 Flashcards
What is a nucleophile?
An electron pair donor
What mechanism do haloalkanes undergo?
Nucleophilic substitution
What is hydrolysis?
A chemical reaction involving water or an aqueous solution of a hydroxide that causes the breaking of a bond in a molecule.
Describe the process of hydrolysis
The nucleophile, OH - approaches the carbon atom attached to the halogen
A lone pair of electrons on the hydroxide ion is attracted and donated to the carbon atom
A new bond is formed between the oxygen atom of the hydroxide ion and the carbon atom
The carbon-halogen bond breaks by heterolytic fission
An alcohol and halide ion are formed
Draw the mechanism for nucleophilic substitution of chloroethane
What are the reaction conditions and reagents for hydrolysis?
Heated under reflux with an aqueous alkali (typically sodium hydroxide)
Examples of nucleophiles
Hydroxide ions
Water molecules
Ammonia molecules
How is the rate of hydrolysis measured?
The rate of reaction can be measured by reacting the haloalkane with water in the presence of aqueous silver nitrate and ethanol.
A precipitate of the silver halide should form.
The time taken for each precipitate to form for different haloalkanes is measured - the fastest time has the fastest rate of reaction
What determines the rate of hydrolysis?
The strength of the carbon-halogen bond
Which halogen has the strongest carbon-halogen bond?
Fluorine, C-F
Which halogen has the weakest carbon-halogen bond?
Iodine, C-I
What is the trend between bond enthalpy of the carbon-halogen bond and the rate of hydrolysis?
Rate of hydrolysis increases as the strength of the carbon-halogen bond decreases
How are halogen radicals produced?
They are produced from a process called photodissociation.
Photodissociation occurs when UV radiation provides sufficient energy to break a carbon-halogen bond in CFCs by homolytic fission to form radicals
Write the equation for the photodissociation of CF2Cl2
How do halogen radicals harm the Earth’s ozone layer?
The halogen radical formed from photodissociation is a very reactive intermediate. It reacts with an ozone molecule, breaking down the ozone into oxygen.
Write down the equations for the two step process of how chlorine radicals react with ozone
What is the overall equation for the breakdown of ozone in the ozone layer?
