4.2.1 Alcohols Flashcards
Are alcohols soluble in water?
- likely to be soluble in water due to similar strength attractions between water and alcohol molecules
- alcohol molecules are able to form hydrogen bonds with water due to polar -OH group
Why does solubility decrease with chain length?
- a larger part of the molecule is made up of non-polar carbon-hydrogen bonds
- the hydrocarbon chain does not form hydrogen bonds with water molecules
Are alcohols polar?
- the O-H functional group is polar due to differences in electronegativities between oxygen and hydrogen
- there is a electron deficient hydrogen that can form hydrogen bonds
Draw a diagram to show the hydrogen bonding in alcohol molecules
See notes
Why are alcohols less volatile than alkanes?
- low volatility = higher bpt
- alcohol molecules have hydrogen bonds between molecules
- alkanes only have London forces between molecules
- more energy is needed to overcome hydrogen bonds as they are stronger than London forces
- alcohols have a higher bpt
What is a primary alcohol?
- an alcohol with one alkyl group attached to C-OH
- e.g. propan-1-ol
Draw a primary alcohol
See notes
(Propan-1-ol)
What is a secondary alcohol?
- an alcohol with 2 alkyl groups attached to C-OH
- e.g. butan-2-ol
Draw a secondary alcohol
See notes
(Butan-2-ol)
What is a tertiary alcohol?
- an alcohol with 3 alkyl groups attached to C-OH
- e.g. methylpropan-2-ol
Draw a tertiary alcohol
See notes
(Methylpropan-2-ol)
Draw reaction for incomplete combustion of pentan-1-ol
See notes
(Insufficient oxygen present for complete oxidation)
Draw reaction for complete combustion of propan-2-ol
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(Plentiful supply of oxygen)
What does a primary alcohol form when oxidised?
- primary alcohol
- aldehyde
- carboxylic acid
- (2 H to be removed = 2 steps)
What does a secondary alcohol form when oxidised?
- secondary alcohol
- ketone
What does a tertiary alcohol form when oxidised?
- no reaction
What are the conditions for the oxidation of primary alcohols?
- acidified potassium dichromate (+heat)
- H2SO4/K2Cr2O7
- reaction carried out under distillation conditions to form an aldehyde
- reaction carried out under reflux to form a carboxylic acid
- oxidising agent represented by [O] in a reaction equation
What colour change occurs during the oxidation of primary alcohols?
- from orange to green
- Cr(VI) = orange
- Cr(III) = green
Draw the oxidation of a primary alcohol to form an aldehyde
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Under distillation conditions
Draw the oxidation of a primary alcohol into a carboxylic acid
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Under reflux
No H2O
Why are distillation and reflux conditions used?
- distillation - as soon as the aldehyde forms it doesn’t have time to form the carboxylic acid
- reflux - this allows the aldehyde to condense back into the reaction flask and carry on reacting
What is the overall equation for the oxidation of primary alcohols?
Primary alcohol + 2[O] -> carboxylic acid + H2O
- Primary alcohol + [O] -> aldehyde + H2O
- Aldehyde + [O] -> carboxylic acid
How are secondary alcohols oxidised?
- form ketones
- carried out under reflux to ensure that all reactant is converted into product
Draw the oxidation of a secondary alcohol to a ketone
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What are the conditions for the elimination of water from alcohols (dehydration)?
- concentrated H3PO4 or H2SO4
- under reflux for about 40mins
What is the equation for the dehydration of alcohols?
See notes
What are the conditions for the substitution of alcohols to give haloalkanes?
- chlorides NaCl/c. H2SO4
- bromides NaBr/c. H2SO4
- iodides NaI/H3PO4
What is the equation for the substitution of alcohols to give haloalkanes?
See notes
