6.1.2 Carbonyl Compounds

Question 1

Is the carbonyl group polar?

Answer 1

• there is an overall dipole as O is more electronegative as the electrons in the covalent bond are attracted to the O
• C=O bond

Question 2

What is the aldehyde functional group?

Answer 2

• the end carbon has a C=O bond and and C-H bond

Question 3

What is the ketone functional group?

Answer 3

• a C=O bond in the middle of the hydrocarbon chain

Question 4

Are carbonyls soluble in water?

Answer 4

• they can form hydrogen bonds with water molecules

Question 5

What is the boiling point of carbonyls?

Answer 5

• permanent dipole-dipole forces between molecules
• higher boiling points than alkenes with similar Mr

Question 6

What reaction produces aldehydes and carboxylic acids?

Answer 6

• acidified potassium dichromate (VI)
• orange dichromate ions turn green Cr3+
• primary alcohols under distillation produces aldehydes + water
• primary alcohols under reflux produces carboxylic acids

Question 7

What reaction produces ketones?

Answer 7

• [O] with secondary alcohols under reflux
• produces ketones and water

Question 8

What is the mechanism for the reaction of carbonyls?

Answer 8

• nucleophilic addition

Question 9

What are the reagents for the reduction of carbonyl compounds?

Answer 9

• using NaBH4 [H] as a reducing agent
• aldehydes is reduced to primary alcohol
• ketone is reduced to secondary alcohol

Question 10

What are the reagents for the reaction of carbonyls to form hydroxynitriles?

Answer 10

• NaCN and acid generates HCN which adds across the C=O to form a hydroxynitrile

Question 11

What is the mechanism for nucleophilic addition for carbonyls to form hydroxynitriles?

Answer 11

See notes

Question 12

What is the test for carbonyl groups?

Answer 12

• add 2,4-DNPH / Brady’s reagent
• orange-yellow precipitate for aldehydes and ketones
• no reaction for carboxylic acids or esters

Question 13

What is the reaction that occurs with Brady’s reagent?

Answer 13

• addition across the double bond an elimination of a water molecule
• condensation reaction

Question 14

How to recognise specific aldehydes or ketone after adding Brady’s?

Answer 14

• precipitates formed have very specific melting points
• can be recrystallised to ensure that crystals are pure and the mpt will be accurate for specific aldehydes or ketone

Question 15

How to test between aldehydes and ketones?

Answer 15

• add Tollen’s reagent (amonnical silver nitrate)
• aldehyde is oxidised to carboxylic acid and forms a silver mirror
• no reaction with ketone as there are no H+ ions that can reduce the silver ions to form solid silver to form the mirror

Question 16

What is the mechanism for nucleophilic addition for the reduction of carbonyls?

Answer 16

See notes