Aldehydes And Ketones

Question 1

What is the functional group of an aldehyde

Answer 1

See notes

Question 2

What is the functional group of a ketone

Answer 2

See notes

Question 3

Physical properties of aldehydes and ketones

Answer 3

1. Normally liquids
2. C=O gives permanent dipole ➡️ dipole dipole forces stronger than vdw ➡️ higher mp
3. Lower bp than alcohols ➡️ can’t H bond with themselves
4. Low RFM = miscible w water ➡️ increased RFM = decrease solubility

Question 4

How to prepare aldehydes

Answer 4

⭕️ Oxidation of primary alcohols
1. Use acidified potassium dichromate (VI) solution
2. Heat and distill to prevent further oxidation to carboxylate acid
3. Colour change orange ➡️ green
4. Chromium +6 to +3
See notes for equation

Question 5

How to prepare ketones

Answer 5

⭕️ Oxidation of secondary alcohols
1. Acidified…
Orange ➡️ green
See notes for eqn

Question 6

What is an addition reaction

Answer 6

Molecule adds to the multiple bond of another molecule to form a single molecule

Question 7

What does aldehyde/ketone + HCN produce

Answer 7

Cyanohydrin
Optically inactive
Racemic
See notes

Question 8

Draw the mechanism for nucleophilic addition HCN to propanone

Answer 8

See notes

Question 9

What is the product of condensation reactions with 2,4 - dinitrophenylhydrozine

Answer 9

Yellow/orange percipitates
(Name of aldehyde/ketone) 2,4-dinitrophenylhydrozine
H2O

Question 10

Abbreviation of condensation reactions

Answer 10

Zine ➡️ zone

Question 11

Draw 2,4 - dinitrophenylhydrozine

Answer 11

See notes

Question 12

Why are condensation reactions the most important method of identifying aldehyde or ketones

Answer 12

1. Derivatives have sharp mp
2. Derivatives easily recrystallised➡️ determine mp
3. Easily obtained at room temp
4. Derivatives high rmm - solid

Question 13

How to test if aldehyde or ketone

Answer 13

Aldehydes oxidised but ketones cannot

Question 14

Write equation and state the colour change when aldehyde is oxidised with acidified…

Answer 14

See notes for eqn
Orange ➡️ green
If ketone then stays orange

Question 15

State the half equation, colour change and conditions for aldehydes oxidised via tollens reagent

Answer 15

See notes eqn
Colourless ➡️ silver
Warmed in clean tt

Question 16

State how fehlings is produced

Answer 16

Solution one = CuSO4 (aq)
Solution two = NaOH(aq)
Mixed and warmed

Question 17

Write half equation and colour change when aldehyde is oxidised with fehlings

Answer 17

See notes equation

Blue solution ➡️ red precipitate

Question 18

What is the reducing agent for aldehydes and ketones. What does if do

Answer 18

Lithal- LiAlH4
Reacts with water so dissolved in dry ether
Reduces carbonyl group
Gently reflexes with ketone/aldehyde

Question 19

What is the product if an aldehyde is reduced by lithal

Answer 19

A primary alcohol

See notes for eqn

Question 20

What happens if a ketone is reduced by lithal

Answer 20

Secondary alcohol produced

Question 21

How do you prepare 2,4 - dinitrophenylhydrazone

Answer 21

See notes

Question 22

What condition is required for both tollens reagent and fehlings solution

Answer 22

Heat