8: Carbonyl Compounds

Question 1

What is a carbonyl group

Answer 1

C=O

Question 2

What does the term carbonyl compound refer to

Answer 2

Aldehydes and ketones

Question 3

What is the oxidising agent for oxidising primary and secondary alcohols

Answer 3

Hot, aqueous, acidic potassium dichromate

Question 4

What does oxidation of a primary alcohol form

Answer 4

Aldehyde

Question 5

What does extended oxidation of a primary alcohol produce

Answer 5

Carboxylic acid

Question 6

What does oxidation of a secondary alcohol form

Answer 6

Ketones

Question 7

What is the main difference between a C=C bond and a C=O

Answer 7

C=O is polar as oxygen is much more electronegative than carbon

Question 8

Why are carbonyl compounds polar

Answer 8

Because the oxygen is very electronegative

Question 9

Why do carbonyl compounds have a higher melting point than alkanes and alkenes of similar size

Answer 9

They can form permanent dipole-dipole bonds due to the dipole

Question 10

Can carbonyl compounds form hydrogen bonds with more of the same carbonyl compound

Answer 10

No, there is no H bonded to the O

Question 11

Can carbonyl compounds form hydrogen bonds with other compounds such as water

Answer 11

Yes

Question 12

What is formed when aldehydes or ketones react with 2,4 DNP

Answer 12

Yellow or orange precipitate

Question 13

How to use 2,4-DNP to identify a specific aldehyde or ketone

Answer 13

• Add 2,4-DNP and collect precipitate by filtration.
• Purify the solid by recrystallisation
• Measure the melting point of the crystals
• Compare m.p. with batabase - to identity the original aldehyde/ ketone

Question 14

What is the process of Recrystallisation

Answer 14

• Dissolve the solid in a minimum amount of hot solvent
• cool the solution: major product crystallises, impurities stay in solution
• collect the crystals by filltration
• Wash crystals with cold solvent
• leave to dry

Question 15

How to distuingish between aldehydes and ketones with aqueous acidic potassium dichromate

Answer 15

Aldehydes will be oxidised

Ketones won’t

Question 16

What is the result of Tollen’s reagent being added to an aldehyde

Answer 16

The aldehyde is oxidised to a carboxylic acid

The silver ions are reduced to metallic silver which is deposited on the side of the container as a shiny silver mirror

Question 17

What does the reduction of a carbonyl form

Answer 17

An alcohol

Question 18

What type of reaction is reduction of carbonyls

Answer 18

Nucleophillic addition

Question 19

What does H^- act as in the reduction of a carbonyl

Answer 19

A nucleophile

Question 20

What does the intermediate in the reduction of a carbonyl act as

Answer 20

Acts as a base as it takes a H^+ from the aqueous solvent water to complete the reaction

Question 21

What is the product of HCN and an aldehyde or ketone

Answer 21

A hydroxynitrile

Question 22

What is the reagent for the reaction of addition of HCN

Answer 22

Acidified aqueous sodium cyanide solution

Question 23

How does CN^- act as a catalyst in the addition of HCN to and aldehyde or ketone

Answer 23

It is used up in the first step but regenerated in the second