Module 6: Chapter 26 (Carbonyls & Carboxylic Acids)
No description yet. This curated deck is ready for daily study.
Card preview (24)
Describe the oxidation reaction of a primary alcohol?
Distillation H+/Cr2O7^2- (acidified dichromate) primary alcohol + [O] -> aldehyde + water orange to green
Describe the oxidation reaction of a secondary alcohol?
Reflux H+/Cr2O7^2- (acidified dichromate) secondary alcohol + [O] -> ketone + water orange to green
Describe the oxidation reaction of a tertiary alcohol?
Reflux H+/Cr2O7^2- (acidified dichromate) NO REACTION TAKES PLACE solution remains orange
Describe the colour change of acidified dichromate?
H+/Cr2O7^2- ORANGE -> [Cr(H2O)5SO4]+ “Cr3+” GREEN
What functional group do aldehydes and ketones both contain and where is it found on the carbon chain?
Both contain the carbonyl functional group C=O • Aldehydes: C=O found at the end of the carbon chain • Ketones: C=O is joined to 2 different carbon atoms in the chain
How do you name aldehydes?
Adding “-al” as a suffix PentanAL, ethanAL etc
How do you name ketones?
Adding “-one” as a suffix Propanone, pentan-2-one, hexan-2-one etc
What happens when aldehydes are further oxidised?
• Aldehydes can be further oxidised to carboxylic acid Aldehyde + [O] -(reflux H+/Cr2O7^2-)-> carboxylic acid
How can scientists distinguish between ketones and aldehydes?
Further oxidation as ketones can’t be further oxidised, meanwhile aldehydes will become carboxylic acids
What are aldehydes reduced into?
Primary alcohols - warmed with aqueous tetrahydridoborate (III) NaBH4 (the reducing agent) aldehydes + 2[H] -NaBH4-> primary alcohols
What are ketones reduced into?
ketones + 2[H] -NaBH4-> secondary alcohols - warmed with aqueous tetrahydridoborate (III) NaBH4 (the reducing agent)
Describe the C=O bond
C=O bond is composed of a σ-bond and a π-bond • the σ-bond is caused by direct overlap of orbitals between the C and O • the π-bond is formed by sideway overlap of p-orbitals above and below the place of C and O atoms
Why is the C=O polar?
• Oxygen is more electronegative than carbon • Electron density in the double bond lies closer to the oxygen atom than to the carbon atom • This makes the carbon end partially positive and the oxygen end partially negative
What happens because of the polar C=O bond?
Due to partially positive bond on carbon, carbonyl compounds will react with nucleophiles in a nucleophilic addition reactions
What is a nucleophile?
An electron pair donor
Draw the mechanism of carbonyl compounds with HCN
Check in book :CN- reacts first with carbon H+ from HCN reacts with O
Describe the reaction of carbonyl compounds with HCN
• HCN adds across C=O bond • HCN is extremely poisonous so NaCN/H2SO4 is used to provide HCN • reaction increases carbon chain length • organic product is a hydroxynitrile • nucleophilic addition reaction
Draw the mechanism of an aldehyde being reduced
check in book H- ion has 2 electrons that are from different atoms and comes from NaBH4 H from H2O makes hydroxyl group with oxygen
Draw the mechanism of a ketone being reduced
check in book H- ion has 2 electrons that are from different atoms and comes from NaBH4 H from H2O makes hydroxyl group with oxygen
What type of reaction is ketone/aldehyde and HCN (H+/NaCN)?
Nucleophilic addition
What reagent can be used to detect presence of a carbonyl group in a ketone or aldehyde?
Brady’s reagent (yellow/orange precipitate)
What is Brady’s reagent?
• Solution of 2,4-DNP dissolved in methanol and sulfuric acid • Detects presence of a carbonyl functional group in ketones or aldehydes only • Positive test results in a yellow/orange precipitate forming
How can the identity of ketones and aldehydes be determined?
• Separate precipitate by filtration from solution • Recrystallise to obtain a pure sample • Measure the melting point • Measured melting point can be compared to known values
What reagent can be used to distinguish between aldehydes and ketones?
Tollen’s reagent