Carbonyl Compounds
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Which of these 2 are oxidised, aldehyde or ketone?
Aldehydes are oxidised to carboxylic acids
What is [o] for aldehydes?
Acidified potassium dichromate (VI), Kr2Cr2O7/H2SO4. Carried out under reflux. Orange to green. Eg: Propanal to propanoic acid CH3CH2CHO + [O] —> CH3CH2COOH
What is the carbonyl group?
C–O
Describe the bonding in the carbonyl group.
C has 2 sigma bonds to other atoms and 1 sigma bond to the O. The p orbitals of C and oxygen creates pi bond above and below the plane of C-O sigma bond
What is the shape around the carbon of a carbonyl group?
Trigonal planar. 3 bonding regions, 0 lone pairs. 120 degrees
Is the C–O bond polar or non polar?
Polar. Difference in electronegativity
What is the C of the C–O bond attacked by and why?
C is partially positive due to more electronegative oxygen atom, so it is vulnerable to attack by nucleophiles (e- pair donors). So addition occurs
What is the reaction mechanism carbonyl groups undergo?
Nucleophillic addition
What are aldehydes reduced to?
Primary alcohols and hydroxide ion. By using NaBH4 as a source of H- (hydride ions). Then adding water 2[H]
What are keytones reduced to?
Secondary alcohols and hydroxide ion. By NaBH4, source of H- ions. Then adding water. 2[H]
What do aldehydes and ketones react with to make hydroxynitriles?
HCN
HCN is toxic. What needs to be done to prevent hazards when using it in reactions?
The carbonyl is reacted with a mixture of H2SO4/NACN (source of cyanide ions)
How do we test for C–O to identify aldehydes and keytones?
Add Brady’s reagent (2,4-DNP) Orange precipitae= positive result for carbonyl
How do you identify aldehyde or keytone?
Purify precipitate from Brady’s reagent via recystallisation. Measure melting point of purified derivative. Compare melting point to known data values
How to distinguish between aldehydes and keytones?
Add Tollen’s reagent (NH3(aq)/AgNO3(aq)/NaOH(ag) ) Heat in 50 degrees water bath. SIlver mirror = -CHO (aldehyde)
What is the reaction taking place in the tollen’s reagent for distinguishing carbonyls?
Ag+ (aq) + e- —> Ag(s) = silver mirror -CHO + [O] —> -COOH
What is tollen’s reagent a mixture of?
Ammonia, silver nitrate and sodium hydroxide. NH3(aq) / AgNO3(aq) / NaOH(ag)