Aldehydes and ketones

Question 1

What can aldehydes be reduced back to

Answer 1

1° alcohol

Question 2

What can ketones be reduced back to

Answer 2

2° alcohol

Question 3

State the:
-reagent
-mechanism
-nucleophile
- condition
of the reduction of aldehydes and ketones

Answer 3

Reduction of Aldehydes and Ketones
Reagent: NaBH4
Mechanism Nucleophilic Addition
Nucleophile H- (a hydride ion)
Condition: Acidic Solvent needed

Question 4

Show the equation of the reduction of butanone to butan-2-ol

Answer 4

CH3CH2COCH3 + 2[H] ——–> CH3CH2CH(OH)CH3

Question 5

State the:
-reagent
-mechanism
-nucleophile
- condition
of the reduction of aldehydes and ketones with -:CN

Answer 5

Reaction of Aldehydes and Ketones with -:CN
Reagent: KCN then HCl
Mechanism Nucleophilic Addition
Nucleophile -:CN
Condition: Acidic needed
Name of product: Hydroxy nitrile

Question 6

State the 2 tests that can be used to distinguish an Aldehyde from a Ketone

Answer 6

Silver Mirror Test
Reagent: Tollen’s Reagent or Ammonical Silver Nitrate
Condition: Warm gently
Observation with Aldehyde Silver mirror Forms
Observation with Ketone No Visible Change

Fehling’s Test
Reagent: Fehling’s Solution
Condition: Warm gently
Observation with Aldehyde Blue Solution to Brick Red Precipitate
Observation with Ketone No Visible Change

Question 7

Why can nucleophilic addition to aldehydes and asymmetircal ketiones result in a racemic mixture of optical isomers?

Answer 7

Planar
Equal chance
Attack
Racemic

-The bonding about a group in an aldehyde and ketone is planar
(little symbol) –c=o
-This means there is a 50:50 chance of the nucleophile attacking from one side of the molecule or the other
-This results in equal proportions of each optical isomer forming, and so a racemic mixture is formed