Aldehydes and Ketones: Reduction

Question 1

What can aldehydes be reduced into?

Answer 1

• Primary alcohols

Question 2

What can ketones be reduced to?

Answer 2

• Secondary alcohols

Question 3

What reducing agent is required for the reduction of aldehydes and ketones?

Answer 3

• NaBH4

- Sodium tetrahydridoborate(III) or sodium borohydride

Question 4

How is the reducing agent usually represented in equations?

Answer 4

• Represented as [H]

Question 5

Give a general equation outlining the reduction of a an aldehyde

Answer 5

• RC(=O)H + 2[H] → RCH(OH)H

Question 6

Give a general equation outlining the reduction of a ketone

Answer 6

• RC(=O)R + 2[H] → RCH(OH)R

Question 7

What reaction mechanism takes place during the reduction of aldehydes and ketones?

Answer 7

• Nucleophilic addition

Question 8

Give a brief overview of what happens during nucleophilic addition reactions

Answer 8

• An H- ion from the reducing agent acts as a nucleophile and attacks the 𝛿+ carbon atom of a carbonyl group

Question 9

Describe what happens during nucleophilic addition for the reduction of aldehydes and ketones

Answer 9

• C=O bond is polar
• H- ion attacks 𝛿+ carbon and donates its lone pair
• C=O bond breaks, electrons transferred to oxygen
• Oxygen has a lone pair and negative charge
• Oxygen donates lone pair to a H+ ion (usually comes from water, or a weak acid)

Question 10

Outline a mechanism for the reduction of propanal into propan-1-ol

Answer 10

• Sorry I don’t have Brainscape Pro so I can’t put a picture

- CGP textbook, page 421

Question 11

Outline a mechanism for the reduction of butanone into butan-2-ol

Answer 11

• Sorry I don’t have Brainscape Pro so I can’t put a picture

- CGP textbook, page 421