Carbonyl Compounds - 6
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What are aldehydes and ketones classified as?
Carbonyl compounds
Where is the carbonyl group located in aldehydes?
At the end of the compound (-CHO)
Where is the carbonyl group located in ketones?
In the middle of the chain (R-C=O-R)
How are aldehydes named?
By adding the ending –al
How are ketones named?
By adding the ending –one
What is the method to prepare aldehydes from primary alcohols?
Oxidising primary alcohols using acidified potassium dichromate
What preparation method is used for aldehydes?
Distillation
What happens to aldehydes if subjected to repeated reflux cycles?
They are further oxidised into carboxylic acids
What is the method to prepare ketones from secondary alcohols?
Refluxing secondary alcohols with acidified potassium dichromate
What reducing agent can be used to reduce aldehydes and ketones?
Sodium borohydride (NaBH4)
Aldehydes are reduced to _______
Primary alcohols
Ketones are reduced to _______
Secondary alcohols
What role does the hydride ion play in the reduction of carbonyl compounds?
It acts as a nucleophile
What is a nucleophile?
A species with a lone pair of electrons attracted to positive charges
What happens during the nucleophilic addition reaction of aldehydes?
The hydride nucleophile attacks the slightly positive carbon atom on the carbonyl functional group
What is formed as a negatively charged intermediate in the nucleophilic addition reaction?
A negatively charged intermediate
What product is formed when hydrogen cyanide reacts with aldehydes and ketones?
A hydroxynitrile
What is used instead of hydrogen cyanide in laboratory preparations?
Sodium cyanide
What test is used to identify the presence of carbonyl functional groups?
2,4-dinitrophenylhydrazine (2,4-DNP) test
What indicates the presence of a ketone or aldehyde in the 2,4-DNP test?
Formation of an orange precipitate
What is the purpose of crystallising the compound after the 2,4-DNP test?
To record its melting point for identification
What is the purpose of Tollens’ reagent in distinguishing between aldehydes and ketones?
It forms a silver mirror if an aldehyde is present
What happens when Tollens’ reagent is added to a ketone?
Nothing will be seen; ketones do not react
What does Tollens’ reagent contain?
Silver nitrate dissolved in ammonia solution