Topic 11: aldehydes + ketones

Question 1

Types of preparation of aldehydes

Answer 1

1) Partial oxidation of primary alcohols
2) Ozonolysis of alkenes
3) Partial reduction of ester
4) Hydroboration-oxidation of terminal alkynes

Question 2

Describe partial oxidation of primary alcohols

Answer 2

• Use PCC = not all the way to carboxylic acid

Question 3

Describe ozonolysis of alkenes

Answer 3

• Every double bonds split = attach O to each new fragment
• Use O3

Question 4

Describe partial reduction of an ester

Answer 4

• DIBAH used to remove -O-R + add H
• R-C=O-H

Question 5

Describe hydroboration-oxidation of alkaynes

Answer 5

• Only terminal alkynes
• Internal alkynes = mixture with ketones
• Using BH3 + H2O2

Question 6

Types of preparation of ketones

Answer 6

1) Oxidation of secondary alcohols
2) Ozonolysis of alkenes
3) Hydroboration-oxidation of internal alkynes
4) Oxymercuration of terminal/internal alkynes

Question 7

Describe oxymercuration of alkynes

Answer 7

• Terminal = methyl-ketone

Question 8

Give oxidation agents for aldehydes

Answer 8

• KMnO4 = hot HNO3
• CrO3 = strongly acidic conditions
• Na/K2Cr2O7 = acid
• Ag2O/Tollen’s = aq ammonia solution NH4OH = alkaline conditions
• Problem = highly acidic conditions = damage other parts of molecule

Question 9

Describe the silver mirror test

Answer 9

• Redox reaction
• Tollen’s reagant
• Aldehyde oxidized →carboxylic acid
• Silver reduced in Ag2O = oxidation number +1→0 silver atoms = reduction

Question 10

Describe the carbonyl group structure

Answer 10

• Polarized = difference in electronegativities C+O
• O-/C+ = C atoms can be attacked by e- rich nucleophiles

Question 11

Explain nucleophilic addition

Answer 11

• Negative nucleophile attacks C+ = single bond forms = Nu-C
• C=O breaks = Nu-C-O⁻
• O- protonated via acid = OH group = alcohol

Question 12

Give nucleophiles

Answer 12

NEGATIVE:
- OH-
- CN-
- H-
NEUTRAL POLAR:
- H2O
- R-OH

Question 13

Describe nucelophilic addition of water

Answer 13

• Aldehyde/ketone + H2O
• O in H2O attacks C
• Double bond O splits and H + OH attaches to each leg
• Products = 1,1-diol + 1,2-diol

Question 14

Describe nucelophilic addition of HCN

Answer 14

• Ketone + HCN/KCN
• :C≡N attacks C
• Double bond O splits
• C-C≡N
• O- → OH

Question 15

Give the transformations of cyanohydrins

Answer 15

1) Reduction of CN group → CH2NH2 = amine
- LiAlH4
2) Hydrolysis of CN → COOH = carboxylic acid
- H2O

Question 16

Explain nucleophilic addition of hydrazine

Answer 16

• Hydrazine = NH2NH2 = early rocket fuel
• Wolff-Kishner reaction
• Reduces C=O → CH2 = ketone → alkane