Chemistry A2 - Carbonyl Compounds Flashcards
What are carbonyl compounds?
Compounds containing a carbonyl group (C=O)
What are the most common carbonyl compounds?
Aldehydes and ketones
Why are aldehydes and ketones soluble in water?
They are able to from hydrogen bonds with water. A hydrogen bond forms between a lone electron pair on the oxygen and a delta positive region on a hydrogen
Why do aldehydes and ketones not from hydrogen bonds with each other?
None of their hydrogens have a delta positive region
How are aldehydes produced?
From the initial oxidation and distillation of a primary alcohol using acidified potassium dichromate
Where is the carbonyl group found on an aldehyde?
On the end of the carbon chain
How are ketones produced?
From the oxidation of secondary alcohols with acidified potassium dichromate
Where is the carbonyl group found on ketones?
On a carbon which is attached to two other carbon atoms
How are carboxylic acids produced?
When primary alcohols are heated under reflux, they will be oxidised further than an aldehyde to form a carboxylic acid (the oxidation of an aldehyde)
What happens when acidified potassium dichromate is reduced and why?
A colour change from orange to green is observed due to a change in the oxidation state of the chromium ion
Why is acidified potassium dichromate an oxidising agent in the oxidation of alcohols?
It allows the alcohol to be oxidised at it itself is reduced
What is the mechanism and reagent by which the carbonyl compounds are reduced back to alcohols?
Mechanism: nucleophilic addition
Reagent: NaBH4 (Sodium borohydride)
What nucleophile does NaBH4 produce?
The H- ion
What are the two nucleophiles which allow nucleophilic addition of carbonyl compounds to occur?
H- and CN-
What is special regarding the use of the CN- nucleophile?
It extends the carbon chain
What does it mean if a molecule has a chiral carbon?
It has optical isomerism
What substance is used to test for the carbonyl group?
2,4-DNP
What happens when aldehydes or ketones react with 2,4-DNP?
A red/orange precipitate is produced
How is 2,4-DNP used to correctly identify a specific aldehyde/ketone?
The precipitate formed is purified by recrystallisation and the melting point of these pure crystals can be compared with melting points of 2,4-dinitrophenylhydrazones of all the common aldehydes and ketones
How are aldehydes identified?
Using Tollen’s reagent. A silver mirror will from if an aldehyde is present, and the solution will remain colourless if a ketone is present
How does Tollen’s reagent work?
It is ammoniacal silver nitrate and it oxidises the aldehyde to a carboxylic acid and reduces silver ions to silver in the presence of an aldehyde, producing the silver mirror
