AC8: Carbonyls
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What is the carbonyl group
C=O
What are the other functional groups that carbonyl refers to
-Aldehydes - Ketones
What is the short hand way of writing aldehyde
-CHO
What do aldehyde compounds name end in
-al
What is the short hand way of writing ketone group
-CO
What do ketone compounds name end in
-one
What is the colour change of the dichromate ions when reduced
• Orange to green
What 2 bonds make up the C=O carbonyl group
• Sigma bond • Pi bond
What is the main difference between the C=C double bond and the C=O double bond
The C=O double bond is polar because oxygen is much more electronegative than carbon
Are carbonyl groups reactive or unreactive with electrophiles
Unreactive
Why do nucelophiles attack the carbonyl group C=O
Since the carbon is slightly positive due to the dipole
Why are aldhehydes and ketones polar
Because of the higher electronegativity of the oxygen, compared to the carbon
Why are the boiling points for carbonyl compounds higher than alkanes and alkenes of similar size
Since the dipoles in carbonyl C=O allows permanent dipole-dipole interactions between molecules which are stronger than London forces
Why do carbonyl compounds have lower boiling points than carboxylic acids and alcohols of similar size
Since carbonyls cannot form hydrogen bonds since there is no H bonded to the oxygen
Why are short chain aldehydes and ketones soluble
Since the oxygen in the C=O can form hydrogen bonds with other compounds such as water
What is the chemical equation for the reduction of ethanal to ethanol
CH3CHO + 2[H] -> CH3CH2OH
What type of reaction is the reaction with NaBH4 and aldehydes and ketones
Reduction reaction
What is the name of the mechanism when NaBH4 reacts with an aldehydes or a ketone
Nucleophilic addition
What is the nucleophile in the compound NaBH4
H- (hydride ion)
Draw the mechanism for the reaction between ethanal and aqueous, acidified sodium cyanide solution
Look in the year 2 notes for answer page 54
Draw the mechanism for the reaction between ethanal and NaBH4
Look in the year 2 notes for answer page 54
Describe the 4 steps in the nucleophilic addition reaction with NaBH4
• The lone pair of electrons from the hydride ion is attracted and donated to the slightly positive carbon atom in the aldehyde or ketone C=O double bond • A dative covalent bond is formed between the hydride ion and the carbon atom of the C=O double bond • The Pi bond in the C=O double bond breaks by heterolytic fission forming a negatively charged intermediate • The oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule. The intermediate has then been protonated to form an alcohol
How do we get the CN- ion
From NaCN and an acid
Why cannot we just use the HCN
Because it’s a lethally toxic gas