Reactions of the Carbonyl Group Aldehydes + Ketones
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What type of reactions do carbonyl compounds commonly undergo?
Nucleophilic addition reactions
Besides nucleophilic addition, what other type of reactions do carbonyl compounds undergo?
Redox reactions
What reagents are used to provide cyanide ions in reactions with carbonyls?
Sodium cyanide (NaCN) or potassium cyanide (KCN)
Why can’t a reaction between carbonyls and cyanide ions be carried out in school labs?
The cyanide ion (CN-) is highly toxic
What is the product formed when a carbonyl compound reacts with cyanide ions followed by dilute acid?
A hydroxynitrile
Why are hydroxynitriles useful in synthesis?
Both the -OH and -CN groups are reactive and can be converted into other functional groups
What is the nucleophile in the reaction of carbonyls with cyanide?
The cyanide ion (CN-)
What is the nucleophile, reagent(s) and conditions involved in a nucleophilic addition reaction involving carbonyl compounds?
Nucleophile: (:CN-) Reagent(s): NaCN or KCN Condtions: Add NaCN or KCN then follow it by dilute hydrochloric acid
Outline the nucleophilic addition reaction involving ketone (propanone) to form a hydroxynitrile Name the hydroxynitrile
Outline, compare and correct where needed Name of hydroxynitrile: 2-hydroxybutanenitrile
Outline the nucleophilic addition reaction involving aldehyde (propanal) to form a hydroxynitrile Name the hydroxynitrile
Outline, compare and correct where needed Hydroxynitrile: 2-hydroxybutanenitrile
Why is the reaction of carbonyl compounds with HCN important in organic synthesis?
It increases the carbon chain length by one carbon
What type of mixture is produced when an aldehyde or an unsymmetrical ketone reacts with HCN?
A racemic mixture of enantiomers (optical isomers)
Why does a racemic mixture form in this reaction?
The planar C=O group allows CN- to attack from above or below with equal probability
What can aldehydes be oxidised to?
Carboxylic acids
Name the common oxidising agent for aldehyde
Acidified potassium dichromate (VI), K2Cr2O7
What reagent can reduce both aldehydes and ketones to alcohols?
Sodium tetrahydridoborate (NaBH4) in aqueous solution
What nucleophile is generated by NaBH4 in aqueous solution?
The hydride ion, :H-
What type of alcohol is formed when an aldehyde is reduced?
A primary alcohol
What type of alcohol is formed when a ketone is reduced?
A secondary alcohol
Outline the reduction mechanism of ethanal into ethanol
Check the correct one and then correct where needs to be done
Outline the reduction mechanism of propanone into propanol
Check the correct one and then correct where needs to be done
What type of mechanism is involved in the reduction of aldehydes and ketones?
Nucleophilic addition
Why does the hydride ion attack the C of the C=O bond, but not C=C bonds?
The C=O carbon is partially positive and attracts nucleophiles, whereas the electron - rich C=C bond repels nucleophiles