Carbonyls and Carboxylic acids Flashcards
(37 cards)
What is the carbonyl group?
C=O
What kind of intermolecular forces do molecules with carbonyl group have?
Permanent dipole-dipole due to the polar C=O bond
How can an aldehyde be oxidised to a carboxylic acid?
Refluxed with K2Cr2O7/H2SO4
Can ketones be oxidised?
No due to the lack of reactivity
How do carbonyl groups undergo nucleophilic addition?
- Due to the polarity of the C=O bond, aldehydes and ketones react with some nucleophiles
- The nucleophile is attracted to the slightly positive carbon
What reducing agent is used to reduce ketones and aldehydes?
NaBH4/H2O
What symbol is used as a reducing agent in the reaction?
2[H]
What symbol is used as an oxidising agent in the reaction?
[O]
What is the product of the reaction of a carbonyl compound with HCN?
A hydroxynitrile
What is the reacting agent used in the reaction of a carbonyl compound with HCN?
H2SO4/NaCN
Why is the reaction of a carbonyl compound and HCN useful?
It provides a mean of increasing the length of the carbon chain
What is the test for detecting carbonyl compounds?
2,4-DNP (Brady’s reagent)
What is the method for detecting an aldehyde and a ketone using 2,4-DNP?
- Add 5cm of 2,4-DNP to a test tube
- Use a dropping pipette add 3 drops of the unknown compound
- If no crystals form, add a few drops of H2SO4
- A yellow/orange precipitate should form indicating the presence of either an aldehyde/ketone
Following the 2,4-DNP how do you distinguish between aldeyhdes and ketones?
Tollen’s reagent
How do you prepare a Tollen’s reagent?
- Add 3cm of aq silver nitrate to a test tube
- Add aq sodium hydroxide to the silver nitrate until a brown precipitate of silver oxide is formed
- Add dilute ammonia solution until the brown precipitate dissolves to form a colourless solution
What is the method for carrying out the test for an aldehyde using Tollen’s reagent?
- Pour 2cm of the unknown solution into a test tube
- Add an equal volume of Tollen’s reagent
- Leave the test tube to stand in a 50 degrees water bath then observe whether any silver mirror is formed
What is the method for identifying an aldehyde or ketone by melting point?
- Filter the yellow/orange solid precipitate
- Re-crystallise the solid
- The melting point of the purified 2,4-DNP is measured and recorded
Describe the solubility in carboxylic acid?
- Carboxylic acids with up to 4 carbon atoms are soluble in water
- As the number of carbon atoms increases, the solubility decreases as the non-polar chain has a greater effect on the overall polarity
What are the strength of carboxylic acids?
They are classified as weak acids
What are the products of a carboxylic acid reacting with a metal in a redox reaction?
A carboxylate and hydrogen gas
What are the products of carboxylic acids with metal oxides?
Salt and water
What is used to test for carboxyl groups?
Carboxylic acid and a carbonate, as the carboxylic acid is sufficiently acidic enough to react with carbonates
What is an acyl group?
C=O attached to an R group
How do you name an acyl chloride?
-anoyl chloride
