Chapter 15 - haloalkanes Flashcards
What are haloalkanes?
Compounds containing the elements carbon, hydrogen and at least one halogen
What is a nucleophile?
An atom or group of atoms that is attracted to an electron deficient area, where it donates a pair of electrons to form a new covalent bond.
Gives examples of nucleophiles
- Hydroxide ions - OH-
- water molecules - H20
- Ammonia molecules - NH3
What is the reaction mechanism called where a nucleophile replaces the halogen in a haloalkane
Nucleophilic substitution
What is the reaction called when the halogen atom is replaced by an -OH group in a haloalkane? (by nucleophillic substitution)
Hydrolysis
What is hydrolysis?
Chemical reaction involving water or an aqueous solution of a hydroxide that causes the breaking of a bond in a molecule
Write the equation for hydrolysis of bromoethane with sodium hydroxide
CH3CH2Br + OH- -> (reflux) CH3CH2OH + Br-
What is the equation for hydrolysis of bromoethane with water?
CH3CH2Br + H2O -> CH3CH2OH + H+ +Br-
What does the rate of hydrolysis depend on?
- Strength of carbon - halogen bond
- Rate of hydrolysis increases as the strength of the carbon- -halogen bond decreases
Briefly describe experiment to test rates of hydrolysis
Add 1-chlorobutane, 1-bromobutane and 1-iodobutane to separate test tubes of ethanol and add aqueous silver nitrate. Observe and record what time each precipitate forms at. 1-chlorobutane forms a white precipitate, 1-bromobutane forms a cream precipitate, 1-iodobutane forms a yellow precipitate.
What is the trend in bond enthalpies down group 7 of their carbon bonds?
Decreases
C-F bond is the strongest
Which haloalkane is hydrolysed fastest: primary, secondary or tertiary?
Tertiary
most stable
reacts by two step mechanism
What are CFCs
Chlorofluoro-carbon
Haloalkane that contains chlorine, fluorine and carbon
all the hydrogens have been replaced
What are the properties of CFCs? What were they used for?
- Very stable (due to carbon - halogen and bond strength), volatile, non- flammeable and non-toxic
- Used in fridges, aerosols cans, dry cleaning and air conditioning
How do CFCs deplete the ozone layer?
UV radiation in stratosphere provides energy to break a carbon-halogen bond in CFCs, breaking C-Cl bond (lowest bond enthalpy) (photodissociation) forming a chlorine radical which reacts with ozone molecules to form oxygen - breaking it down.
Write down the equations showing how CFCs break down the ozone layer
CF2Cl2 -> CF2Cl. + Cl. propagation Cl. + O3 -> ClO. + O2 ClO. + O -> Cl. + O2 chlorine radical regenerated cycle.
Why do CFCs take years to reach ozone layer?
Very stable
What other radicals cause ozone depletion?
Nitrogen oxide radicals
Formed during lightning strikes and aircraft travel
When were CFCs removed?
1987 Montreal protocol
Write 2 equations to show how NO catalyses the ozone breakdown?
NO + O3 -> NO2 + O2
NO2 + O -> NO + O2
