Carboxylic acids and esters
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What is the functional group of a carboxylic acid?
The carboxyl group, written as -COOH
Where can the carboxylic acid functional group be located on a carbon chain?
Only at the end of a carbon chain
Which two familiar functional groups are present in a carboxylic acid?
A carbonyl group (C=O) and a hydroxyl group (-OH)
Why is the -OH group in carboxylic acids more acidic than in alcohols?
It is attached to a carbonyl group, which increases the acidity
What suffix is used to name carboxylic acids?
-oic acid
Name HCOOH
Methanoic acid
Name CH3CHBrCOOH
2-bromopropanoic acid
How are substituents numbered in carboxylic acids?
Numbering starts frm the carboxyl carbon (C=O) as carbon-1
Name CH3COOH
Ethanoic acid
Name CH3CH(CH3)CH2COOH
3-methylbutanoic acid
What suffix is used when the -COOH group is attached to a benzene ring?
-carboxylic acid
When naming a benzene ring with a –COOH group, is the carbon of the –COOH counted as part of the ring?
No
Why are carboxylic acids soluble in water (up to butanoic acid?)
Because the -COOH group can form hydrogen bonds with water molecules
Draw a molecule of carboxylic acid (ethanoic aicd) forming hydrogen bonds with water Showing all partial charges
Ethanoic acid hydrogen bonded to two water molecules
Outline a pair of carboxylic acid hydrogen bonding ->The product that is formed, what is it called?
Two ethanoic acids bonded to each other. Name: dimer
Why are longer chain carboxylic acids less soluble in water?
The long hydrocarbon chain disrupts the hydrogen bonding between water molecules, replacing them with weaker van der Waals forces
Why do carboxylic acids have higher melting points than alkanes of similar Mr?
Carboxylic acids form hydrogen bonds with each other in the solid state
Name two methods for determining the melting point of a carboxylic acid
Using a Thiele tube or by finding it electrically
How are esters derived from carboxylic acids?
By replacing the H atom of the -OH group with an alkyl or aryl group
What is the general formula of an ester?
RCOOR’
Name the compound drawn (CH3COOCH3)
Check you answer (methyl ethanoate)
How are esters named?
Name starts with the alkyl (or aryl) group that replaced the hydrogen, followed by the parent acid name ending in -oate
Compare the boiling points of esters with alcohols of similar Mr (H bonds)
Esters have lower boiling points than alcohols because they cannot form hydrogen bonds between their own molecules, whereas alcohols can, giving them stronger intermolecular forces
Why do esters have higher boiling points than alkanes of similar Mr? (Esters - two IF - polar, Alkanes - 1 IF)
Esters are polar molecules and have dipole - dipole interactions in addition to van der Waals forces, unlike alkanes which only have van der Waals forces, which are weaker and therefore require less energy to overcome