What is the carbonyl functional group?

The carbonyl functional group consists of a carbon-oxygen double bond (C=O).


The carbonyl group is present in aldehydes and ketones.

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Describe the position of the carbonyl functional group in an aldehyde.

In an aldehyde, the carbon atom of the carbonyl functional group is located at the end of a carbon chain, bonded to at least one hydrogen atom.


The displayed formula of the aldehyde propanal is:

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Describe the position of the carbonyl functional group in a ketone.

In ketones, the carbon atom of the carbonyl functional group is bonded to two other carbon atoms in the carbon chain.


The displayed formula of the ketone propanone is:

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What suffixes are used to name aldehydes and ketones?

Aldehydes are named using the suffix -al.

Ketones are named using the suffix -one.


The carbonyl carbon is counted as part of the carbon chain of the root, e.g., HCHO is methanal. 

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How are aldehydes prepared?

Aldehydes are made from the oxidation of a primary alcohol using acidified K2Cr2O7, gentle heating and distillation.

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Why do carbonyl compounds react with nucleophiles?

The C=O bond is polarised, with the carbon being partially positive (and the more electronegative oxygen being partially negative). The partially positive carbon is suspectible to attack by nucleophiles.

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Why do carbonyl compounds undergo addition reactions?

Carbonyl compounds are unsaturated because they contain a C=O double bond - this means they can undergo addition reactions.

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Describe how aldehydes and ketones can be distinguished using acidified potassium dichromate(VI).

Aldehydes can be oxidised to carboxylic acids when refluxed with acidified potassium dichromate. During this process, the solution turns from orange to green.

Ketones, however, do not undergo oxidation with acidified potassium dichromate so the solution remains orange.

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Name and outline the mechanism for the reaction above.

This mechanism is nucleophilic addition.


Aldehydes also react with H- via the same mechanism.

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What is the general equation for the reduction of a ketone, RCOR', with a reducing agent, [H]?

RCOR' + 2[H] ➔ RCH(OH)R'

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Name the reducing agent used in the reduction of aldehydes and ketones to alcohols.

Sodium borohydride (NaBH4)

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Outline the mechanism for the reaction above.

Ketones also react with CN- via the same mechanism.

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Name the mechanism in the reaction between carbonyl compounds and hydrogen cyanide.

Nucleophilic addition

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Why is the reaction between carbonyl compounds and hydrogen cyanide useful?

This reaction is useful as it provides a means of increasing the length of the carbon chain by 1 carbon atom.

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What type of product is formed in the reaction of an aldehyde or ketone with hydrogen cyanide?

A hydroxynitrile is formed.


The two functional groups of a hydroxynitrile are a hydroxyl group (-OH) and a nitrile group (C≡N).

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How and why is hydrogen cyanide generated in situ for the reaction with aldehydes and ketones?


Hydrogen cyanide is generated in situ for the reaction with aldehydes and ketones by mixing potassium cyanide or sodium cyanide with a dilute acid. This is done because HCN is a toxic gas, and generating it in situ allows for safer handling and use in the reaction.

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What is the general equation for the reaction of an aldehyde (RCHO) with hydrogen cyanide (HCN)?

RCHO + HCN ➔ RCH(OH)CN

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How are ketones prepared?

Ketones are made from the oxidation of a secondary alcohol using acidified K2Cr2O7 and heating under reflux.

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