6.1.2 - Carbonyl compounds

Question 1

What is the difference between a ketone and aldehyde ?

Answer 1

• The positioning if the -CO group

Question 2

N’t pure carbonyls form hydrogen bonds with each other ?

Answer 2

Pure carbonyls can’t form hydrogen bonds with each other because they lack -NH, -OH, or -FH bonds. Instead, they interact via permanent dipole-dipole forces due to the polar C=O bond.

Question 3

Explain what you understand about the solubility of carbonyls in water

Answer 3

• smaller carbonyls can form hydrogen bonds with water because the oxygen in the C=O bond has lone pairs, allowing it to accept hydrogen bonds from water molecules. This is why smaller aldehydes and ketones are soluble in water.
• However, as the carbonyl chain gets longer (with larger alkyl groups), the molecule becomes less soluble in water. This happens because the non-polar alkyl group dominates, reducing the molecule’s overall ability to interact with water.

Question 4

What are aldehyde oxidised to ?

Answer 4

To carboxylic acids

Question 5

What can ketones be oxidised to ?

Answer 5

They can’t be further oxidised.

Question 6

What is used to reduce as aldehydes back into alcohols

Answer 6

NaBH₄ (sodium tetrahydriborate
- Nucleophilic addition

Question 7

What is used to reduce as ketones back into alcohols

Answer 7

NaBH₄ (sodium tetrahydriborate)
- Necleophilic addition

Question 8

How does the mechanism for the reduction of carbonyls look like ?

Answer 8

Question 9

How are carbonyls converted into hydroxynitriles

Answer 9

• Sodium cyanide and dilute sulphuric acid

Question 10

Draw the mechanism for carbonyls into hydroxynitrile’s

Answer 10

Question 11

Why do we use potassium cyanide, and how do we control the risks. ?

Answer 11

• HCN is difficult to contain
• Use a fume cupboard

Question 12

How do we distinguish between an aldehyde and a ketone ?
Also how would you prepare the test ?

Answer 12

By using tollen’s reagents
- Aldehyde : Silver mirror
- Ketone : No precipitate formed

Question 13

How do we test for if a carbonyl is present

Answer 13

2,4-DNP an orange precipitate will be formed if a carbonyl is present

Question 14

What results from the 2,4-DNP can we use to identify the different carbonyl compounds present ?

Answer 14

The melting points.
- The melting point of the crystal formed can be used to
help identify which carbonyl was used. Take the melting
point of orange crystals product from 2,4-DNP. Compare
melting point with known values in database