Aldehydes And Ketones Flashcards
What is the functional group of an aldehyde
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What is the functional group of a ketone
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Physical properties of aldehydes and ketones
- Normally liquids
- C=O gives permanent dipole ➡️ dipole dipole forces stronger than vdw ➡️ higher mp
- Lower bp than alcohols ➡️ can’t H bond with themselves
- Low RFM = miscible w water ➡️ increased RFM = decrease solubility
How to prepare aldehydes
⭕️ 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
How to prepare ketones
⭕️ Oxidation of secondary alcohols
1. Acidified…
Orange ➡️ green
See notes for eqn
What is an addition reaction
Molecule adds to the multiple bond of another molecule to form a single molecule
What does aldehyde/ketone + HCN produce
Cyanohydrin
Optically inactive
Racemic
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Draw the mechanism for nucleophilic addition HCN to propanone
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What is the product of condensation reactions with 2,4 - dinitrophenylhydrozine
Yellow/orange percipitates
(Name of aldehyde/ketone) 2,4-dinitrophenylhydrozine
H2O
Abbreviation of condensation reactions
Zine ➡️ zone
Draw 2,4 - dinitrophenylhydrozine
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Why are condensation reactions the most important method of identifying aldehyde or ketones
- Derivatives have sharp mp
- Derivatives easily recrystallised➡️ determine mp
- Easily obtained at room temp
- Derivatives high rmm - solid
How to test if aldehyde or ketone
Aldehydes oxidised but ketones cannot
Write equation and state the colour change when aldehyde is oxidised with acidified…
See notes for eqn
Orange ➡️ green
If ketone then stays orange
State the half equation, colour change and conditions for aldehydes oxidised via tollens reagent
See notes eqn
Colourless ➡️ silver
Warmed in clean tt
State how fehlings is produced
Solution one = CuSO4 (aq)
Solution two = NaOH(aq)
Mixed and warmed
Write half equation and colour change when aldehyde is oxidised with fehlings
See notes equation
Blue solution ➡️ red precipitate
What is the reducing agent for aldehydes and ketones. What does if do
Lithal- LiAlH4
Reacts with water so dissolved in dry ether
Reduces carbonyl group
Gently reflexes with ketone/aldehyde
What is the product if an aldehyde is reduced by lithal
A primary alcohol
See notes for eqn
What happens if a ketone is reduced by lithal
Secondary alcohol produced
How do you prepare 2,4 - dinitrophenylhydrazone
See notes
What condition is required for both tollens reagent and fehlings solution
Heat
