17.1Aldehydes & Ketones

A set of flashcards reviewing the synthesis, reactions, and tests for aldehydes and ketones in chemistry.

What are aldehydes and ketones classified as?

Carbonyl compounds containing a C=O group.

How are aldehydes prepared from alcohols?

By the oxidation of primary alcohols using oxidising agents.

What oxidising agent is represented by K2Cr2O7 and its color change?

Potassium dichromate, which is orange and reduces to green chromium(III) ions.

What happens to potassium manganate (VII) during oxidation?

It is purple and reduces to colorless manganese(II) ions.

How do you synthesize an aldehyde from a primary alcohol?

By warming the primary alcohol with an oxidising agent and distilling it off as soon as it forms.

What is the difference in oxidation of primary alcohols and secondary alcohols?

Primary alcohols form aldehydes which must be distilled off, while secondary alcohols form ketones which do not require immediate distillation.

What happens if an aldehyde is not distilled off during oxidation?

It will be further oxidised to a carboxylic acid.

What type of alcohols are reduced to primary alcohols?

Aldehydes are reduced to primary alcohols.

What do ketones become upon reduction?

Ketones are reduced to secondary alcohols.

What is formed when aldehydes and ketones undergo nucleophilic addition with HCN?

Hydroxynitriles are formed.

What is a key characteristic of the nucleophilic addition of HCN to an aldehyde?

It always forms a chiral hydroxy nitrile compound.

What is the purpose of the 2,4-DNPH reagent?

It detects the presence of carbonyl compounds.

What visible result indicates a positive test for carbonyls using 2,4-DNPH?

A deep-orange precipitate forms.

What is Fehling's solution used for?

To detect the presence of aldehyde groups; it turns from blue to red when a positive reaction occurs.

What reaction occurs with Tollens' reagent and aldehydes?

Aldehydes are oxidised to carboxylic acids resulting in a silver mirror.

What type of compounds react to form iodoform?

Methyl ketones lead to the formation of a yellow precipitate (iodoform).