4.3 - Alcohols and haloalkanes Flashcards
(49 cards)
What are alcohols ?
They are a homologous series with the functional group -OH ( hydroxyl group )
How do you name alcohols ?
- Name ends in -ol/ starts with hydroxy-
- Count from end nearest -OH unless C=C present ( then count from end nearest of double bond )
What are the physical properties of alcohols in comparison to Alkanes ( of the same chain length ) ?
- Less volatile
- High melting points
- Greater water solubility
Explain why alcohols have a higher melting point than alkanes ( of the same chain length ) ?
- Alkanes have non-polar bonds because the electronegativity of hydrogen and carbon are very similar
- Alkanes are therefore non-polar
- Therefore there are only weak London forces between alkane molecules which don’t require a lot of energy to overcome
- Alcohols have a polar O—H bond because of the difference in electronegativity of the oxygen and hydrogen atoms
- Alcohols are therefore polar
- Therefore, the are weak London forces and strong hydrogen bonds between molecules which require more energy to overcome resulting in higher boiling point
Explain why alcohols are less volatile than alkanes ( of the same chain length ) ?
- More energy is required to overcome strong hydrogen bonds and weak London forces between alcohol molecules than to overcome only weak London forces between alkane molecules
- Therefore, alcohols are less volatile than alkanes
Explain why alcohols are more water soluble than alkanes ( of the same chain length ) ?
- Alkanes are non-polar molecules and cannot form hydrogen bonds with water
- Alcohols are polar molecules that can form hydrogen bonds with water between the polar -OH group and water molecule
- Therefore they are more water soluble than alkanes
Explain the effect of size on water solubility of alcohols?
- As the size of the alcohol increases, the size of the R group on the alcohol increases
- A long-chain alcohol can only form hydrogen bonds between the polar -OH group and water molecule, the rest of the molecule is non-polar and cannot form hydrogen bonds with water between
- As the hydrocarbon chain increases in size, the influence of the -OH group becomes relatively smaller, and the solubility descreases
Draw a diagram showing formation of hydrogen bonds between alcohol molecules ?
Draw a diagram showing hydrogen bonds forming between alcohol and water molecules ?
What are the different types of alcohols ?
- Primary alcohols
- Secondary alcohols
- Tertiary alcohols
Draw the structure of a primary, secondary and tertiary alcohol ?
What are the different reactions with alcohols ?
- Combustion of alcohols
- Oxidation of alcohols
- Dehydration of alcohols
- Substitution reactions
What are the features of the combustion of alcohols ?
- Alcohols undergo complete combustion in a plentiful supply of Ov2, forming COv2 and Hv2O
- The reaction is exothermic
- As the number of carbons in the alcohol molecule increases, the amount of energy that is released per mole increases
Write an equation to show ethanol undergoing complete combustion ?
Cv2Hv5OH + 3Ov2 —> 2COv2 + 3Hv2O
Do you know how to write and balance equations showing combustion of alcohols ?
Yes
How is an oxidising agent written in an equation showing the oxidation of alcohols ?
The symbol [O] is used to symbolise an oxidising agent
What are the different oxidations of alcohols ?
- Oxidation of primary alcohols to from aldehydes
- Oxidation of primary alcohols to form carboxylic acids
- Oxidation of secondary alcohols to form ketons
State the reagents, conditions and observations for the oxidation of primary alcohols to form aldehydes ?
- Reagents : Primary alcohol, acidified potassium dichromate (VI) [ Kv2Crv2Ov7 / H+ ]
- Conditions : Distillation
- Observations : Solution goes from orange to green
Write an equation to show the oxidation of primary alcohol to form aldehydes ( ethanol ) ?
State the reagents, conditions and observations for the oxidation of primary alcohols to form carboxylic acids ?
- Reagents : Primary alcohol, acidified potassium dichromate (VI) [ Kv2Crv2Ov7 / H+ ]
- Conditions : Reflux
- Observations : Solution goes from orange to green
Write an equation to show the oxidation of primary alcohol to form carboxylic acids ( ethanol ) ?
State the reagents, conditions and observations for the oxidation of secondary alcohols to form ketones ?
- Reagents : Secondary alcohol, acidified potassium dichromate (VI) [ Kv2Crv2Ov7 / H+ ]
- Conditions : Reflux
- Observations : Solution goes from orange to green
Write an equation to show the oxidation of secondary alcohols to form ketones ( propane-2-ol ) ?
Explain why tertiary alcohols cannot be oxidised / no reaction occurs ?
A strong carbon-carbon bond would have to be broken in order to oxidise a tertiary alcohol
