Carbonyl Compounds Flashcards
What is
the carbonyl group?
C=O
What are
carbonyl compounds?
Organic compounds that have the carbonyl group
What two homologous series are considered
when talking about carbonyl compounds?
Aldehydes & Ketones
What is another name for
an Aldehyde?
an Alkanal
What is another name for
a Ketone?
an Alkanone
What is the general formula for an aldehyde?
RCOH
What is the general formula for a ketone?
RCOR’
What is more reactive: an aldehyde or a ketone?
An aldehyde
What reactions do carbonyl compounds typically undergo?
Nucleophilic addition reactions
the nucleophiles are attracted to the electron-rich C=O
Why do carbonyl compounds undergo nucleophilic addition reactions?
The carbon in the C=O bond has a partially positive charge due to the electronegativity difference between carbon and oxygen
Therefore the carbon there is an electrophile (e- deficient specie)
Can aldehydes be oxidised?
Yes. They oxidise to carboxylic acids
Can ketones be oxidised?
No
Why can’t ketones be oxidised?
Oxidation is also the removal of hydrogen, in the ketone structure, RCOR, there is no hydrogen directly bonded to the carbon atom to be removed
Can aldehydes be reduced?
Yes. They are reduced to PRIMARY alcohols
Can ketones be reduced?
Yes. They are reduced to SECONDARY alcohols
How are aldehydes produced?
The oxidation of primary alcohols
What are reaction conditions for the production of aldehydes by the oxidation of primary alcohols
- Distillation
- Heating of the reacting system
- Acidified K2Cr2O7 / Acidified KMnO4
In what other way
can aldehydes be produced?
The (incomplete) reduction of carboxylic acids
How are ketones produced?
The oxidation of secondary alcohols
What are reaction conditions for the production of ketones by the oxidation of secondary alcohols
- Heating of the reacting system
- Acidified K2Cr2O7 / Acidified KMnO4
What are both aldehydes and ketones reduced to?
Alcohols
Name the nucleophile
that can reduce aldehydes and ketones to alcohols
The hydronium ion (H-)
Name the 2 nucleophiles
that can reduce aldehydes and ketones reduced to alcohols
- The water molecule
- The hydroxide group
What type of isomerism
relates an aldehyde to its corresponding ketone
(by that I mean they have the same number of carbons)
Structural Isomerism
Specifically functional group isomerism
What is
a symmetric ketone?
A ketone with the same number of carbons on either side of the carbonyl group
Eg: Propanone
What is
an asymmetric ketone?
A ketone with an unequal number of carbons on either side of the carbonyl group
Can aldehydes be symmetric or asymmetric?
No
Why can’t aldehydes be symmetric or asymmetric?
Because they are formed from primary alcohols that have only one other alkyl group attached to them. The carbonyl group is always on the terminal carbon
What result is expected
in the reaction of carbonyl compounds with 2,4-dinitrophenylhydrazine?
There will be a red-orange precipitate
Do carboxylic acids
produce any precipitate with 2,4-dinitrophenylhydrazine?
No
What is the limitation
of the reaction of carbonyl compounds with 2,4-dinitrophenylhydrazine?
It does not differentiate between aldehydes and ketones, it just shows the presence of the carbonyl group
What type of reaction is the
reaction of carbonyl compounds with 2,4-dinitrophenylhydrazine?
A condensation reaction
A molecule of water is eliminated
How can we differentiate between
aldehydes and ketones?
Using the Tollen’s test
What is observed
when aldehydes react with Tollen’s reagent?
A silver precipitate is formed on the walls of the test tube
Tollen’s reagent contains silver ions which are reduced to metallic silver when they react with the aldehyde.
What is observed
when ketones react with Tollen’s reagent?
Nothing
Ketons do not react with Tollen’s reagent.
What difference between aldehydes and ketones
is typically exploited when using the Tollen’s test?
Aldehydes are readily oxidised and ketones are not, hence, they do not react with Tollen’s reagent
What other solution
can you use to distinguish between aldehydes and ketones besides Tollen’s reagent?
Fehling’s solution
What is observed
when ketones react with Fehling’s solution?
Nothing
Ketones do not reduce Fehling’s solution, so the blue coloured Cu2+ ions remain
What is observed
when aldehydes react with Fehling’s solution?
The solution turns from blue to (brick) red
Fehling’s solution contains Cu2+ ions which are **reduced to Cu+ ions ** when they react with the aldehyde. Copper (I) is brown in colour
What is observed
when ketones react with Acidified potassium dichromate?
No visible change
What is observed
when aldehydes react with Acidified potassium dichromate?
The solution turns from orange to green
Acidified potassium dichromate is an oxidising agent; oxidising the aldehyde to an alkanoic acid and getting reduced from Cr6+ to Cr3+ in the process.
What is the precipitates
when aldehydes react with Fehling’s solution?
Copper (I) oxide (Cu2O)
What are the reaction conditions
for an aldehyde to react with Fehling’s solution?
The solution must be warmed
What are the reaction conditions
for an aldehyde to react with Acidified potassium dichromate?
The reacting system must be warmed
