Alcohols and haloalkanes

What is the classification of alcohols

• primary: OH group is attached to a carbon with 1 alkyl group

• secondary: OH group is attached to a carbon with 2 alkyl groups

• tertiary: OH group is attached to a carbon with 3 alkyl groups

What is the trend in boiling points as chain length increases

• bp increases as chain length increases

• more surface area contact points between the molecules

• more London dispersion forces between molecules

• more energy required to break the LDFs

What is the trend in boiling point as branching increases

• as alcohol becomes more branched the molecules become less closely packed together

• less surface area contact points between the molecules

• less LDFs between molecules

• less energy required to break the forces

What is the trend in bp between propane and propanol

• in propane there are weak LDFs between molecules whereas in propanol the molecules are held together by stronger hydrogen bonds between molecules

• hydrogen bonds require more energy to break

• propanol has higher boiling point than propane

Why are alcohols soluble in water

• alcohols form hydrogen bonds with H2O molecules

What is the trend in solubility as chain length increases

• solubility decreases as chain length increases

• a large part of the molecule is made up of a non-polar hydrocarbon chain

• the non-polar chain does not form hydrogen bonds with H2O

What are the reagents and conditions needed for the oxidation of alcohols and what is the observation

• acidified potassium dichromate (IV), H+/K2Cr2O7: orange → green

• sulfuric acid, H2SO4

• distil or reflux

What is distillation

• liquid is heated then the vapour (volatile component) is cooled and collected in a separate flask to reaction mixture

• products have low boiling points

What is reflux

• continuous boiling of reactants to prevent products escaping

• products have high boiling points

How do you go about oxidation equations

• oxygen is added and water is removed from the carbon with the -OH group attached

What does a primary alcohol produce in distilled conditions

• aldehyde

• 1:1 ratio of oxidising agents and water molecules per aldehyde functional group

What does a primary alcohol produce in reflux conditions

• carboxylic acid

• 2:1 ratio of oxidising agents and water molecules per carboxyl functional group

What is the overall equation of primary alcohols

• primary alcohol → 1. aldehyde (partial oxidation) → 2. carboxylic acid (full oxidation)

• 2. does not produce any water molecules

• total of two oxidising agents required (for reflux)

Why do aldehydes have lower boiling points compared to alcohols and carboxylic acids

• aldehydes do not have hydrogen bonding between molecules compared to alcohols and carboxylic acids

• they have weaker permanent dipole-permanent dipole forces between molecules so they can distill off easily

What does a secondary alcohol produce in reflux conditions

• ketone

• 1:1 ratio of oxidising agents to water molecules per ketone functional group

What is the dehydration of alcohols and what are the reagents and conditions

• alcohol → alkene + water

• concentrated H2SO4/H3PO4

• reflux at 180°

What is the hydrolysis of haloalkanes with water and what are the reagents and conditions required

• haloalkane + water → alcohol + hydrogen halide

• water, heat

What is the hydrolysis of haloalkanes with alkalis and what are the reagents and conditions required

• haloalkane + alkali → metal halide + alcohol

• aq. alkali, heat

What is the explanation of nucleophillic substitution

• hydroxide ion has a lone pair of electrons which are attached to the partially positive carbon atom

• new sigma bond formed between hydroxide ion and carbon atom

• carbon-halogen bond forms by heterolytic fission - both electrons from bond move to the halogen, forming a halide ion

What can react with haloalkanes and why

• one or more lone pair of electrons

• due to large difference in electronegativity

What are the main examples of CFCs and their uses

• CHFCl2 - refrigerant

• CF3Cl - aerosol propellant

• CBrClF2 - fire extinguisher

What are properties of CFCs

• low reactivity

• high volatility

• non toxic

Why have CFCs been blamed for the damage to environment

• thins the ozone layer

• ozone layer absorbs harmful UV radiation to protect organisms

• however it breaks down more easily in the presence of CFCs

• CFCs break up in atmosphere to form radicals which catalyse the breakdown of the ozone layer

Outline the stages of the mechanism for CFCl2 breaking down ozone

• initiation: CF2Cl2 → CF2Cl• + Cl•

• propagation 1: Cl• + O3 → ClO• + O2

• propagation 2: ClO• + O → O2 + Cl•

• overall equation: O3 + O → + 2O2

When is nitrogen oxide produced

• in high temperatures of combustion, N2 + O2 react to form NO

• when lightning is produced

Outline the stages of the mechanism for NO breaking down ozone

• NO• + O3 → NO2• + O2

• NO2• + O → O2 + NO•

• O3 + O → 2O2

Which bond breaks in a CFC and why

• C-Cl bond

• lower bond enthalpy / weaker than C-F bond

• requires less energy to break

Explain what happens to rate of hydrolysis of haloalkanes down group 7

• rate of reaction increases

• atoms get larger down group 7

• bonding electrons further from nucleus

• less nuclear attraction

• lower mean bond enthalpies so C-X bond is easier to break

What is the synthesis of a chloroalkane

• alcohol + HCl → chloroalkane + water

What is the method to separate and purify the organic product

• using a funnel, pour reaction mixture into separating funnel and ensure the tap is closed

• slowly add 10cm3 of 5% hydrogencarbonate solution into separating funnel

• put on stopper and shake gently, then release the gas

• add 10cm3 of distilled water to separating funnel and shake again

• allow the layers to separate then run off the aq layer and discard it

• allow organic later to run into clean 100cm3 comical flask

• add drying agent (sodium sulfate) to remove any traces of water

• filter to collect organic product

• redistil

Why is sodium hydrogen carbonate added to the mixture

• to neutralise any excess acid

How do you determine the aqueous layer

• when water is added, both lines increasing in size means aq layer is at the bottom

• if top line is only increasing, aq layer is at the top

• the bottom aq layer is always discarded

How do you check if the organic product is pure

• check the boiling point of the product

• redistil at that specific temperature

How do you identify the organic layer using waters density of 1gcm-3

• organic layer has density above 1 = bottom layer

• organic layer has density below 1 = top layer