An aldehyde is a carbonyl compound in which the C=O group is positioned at the end of the carbon chain, with the general formula RCHO.

What is the 2,4-DNPH test ?

The 2,4-DNPH test is a test for carbonyl compounds (aldehydes and ketones) in which 2,4-dinitrophenylhydrazine reacts with the C=O group in a condensation reaction to form an orange or yellow precipitate. The melting point of the precipitate identifies the specific carbonyl compound.

What is the position of the carbonyl group in an aldehyde compared to a ketone, and how does this affect their naming?

In an aldehyde , the C=O group is always at carbon-1 (the end of the chain), so the '1' is not included in the name (e.g. ethanal). In a ketone , the C=O group is always in the middle of the chain, so its position must be numbered (e.g. pentan-2-one).

How can acidified potassium dichromate(VI) be used to distinguish between an aldehyde and a ketone?

When warmed with acidified potassium dichromate(VI), an aldehyde is oxidised to a carboxylic acid and the solution changes from orange to green . A ketone is not oxidised under these conditions, so there is no colour change .

True or False? Aldehydes and ketones can hydrogen bond with each other.

False. Aldehydes and ketones have no O−H or N−H bonds, so there is no δ+ hydrogen available for hydrogen bonding between their own molecules. They experience permanent dipole-dipole interactions and London forces only.

True or False? Warming a ketone with Tollens' reagent produces a silver mirror.

False. Ketones cannot be oxidised by Tollens' reagent because they have no readily available hydrogen atom on the carbonyl carbon. Only aldehydes produce a silver mirror with Tollens' reagent.

A ketone is a carbonyl compound in which the C=O group is positioned in the middle of the carbon chain, flanked by two alkyl groups, with the general formula RCOR'.

What is the silver mirror test (Tollens' test)?

The silver mirror test (Tollens' test) is a test using [Ag(NH 3 ) 2 ] + (aq) to distinguish aldehydes from ketones. An aldehyde reduces the silver(I) complex ion to metallic silver, forming a silver mirror on the inside of the tube. A ketone gives no reaction.

Aldehydes and ketones have .......... boiling points than their equivalent alcohols because they cannot form .......... bonds with each other.

Aldehydes and ketones have lower boiling points than their equivalent alcohols because they cannot form hydrogen bonds with each other.

When reduced with LiAlH 4 in dry ether, an aldehyde forms a .......... alcohol and a ketone forms a .......... alcohol.

When reduced with LiAlH 4 in dry ether, an aldehyde forms a primary alcohol and a ketone forms a secondary alcohol.

What is the carbonyl group ?

The carbonyl group is a C=O functional group found in aldehydes and ketones. The oxygen is more electronegative than carbon, creating a dipole with a δ+ carbon and a δ− oxygen.

What does a positive iodoform test indicate, and what is the positive result?

A positive iodoform test indicates the presence of a methyl ketone (CH 3 CO− group) or ethanal . The positive result is a yellow precipitate of tri-iodomethane (CHI 3 ), formed when the compound is heated with an alkaline solution of iodine.

Why do smaller aldehydes and ketones dissolve in water, but larger ones do not?

Smaller aldehydes and ketones dissolve in water because their δ− oxygen atom uses lone pairs to form hydrogen bonds with the δ+ hydrogen of water molecules. Larger carbonyl compounds have longer hydrocarbon chains that disrupt water's hydrogen bonding without forming their own, so the energy cost of dissolving exceeds the energy gained.

Define nucleophilic addition .

Nucleophilic addition is a reaction in which a nucleophile attacks the δ+ carbon of a polarised C=O group, forming a new bond and adding across the double bond to give a single-bonded product.

True or False? The simplest ketone is propan-2-one.

True. Propan-2-one (CH 3 COCH 3 ) is the simplest ketone because a ketone requires an alkyl group on each side of the carbonyl carbon, which means a minimum of three carbon atoms.

True or False? The 2,4-DNPH test gives a positive result with carboxylic acids.

False. The 2,4-DNPH test is selective for aldehydes and ketones. Carboxylic acids and esters also contain C=O groups but do not react with 2,4-DNPH — they do not possess an aldehyde or ketone functional group .

What is observed when Fehling's solution is warmed with an aldehyde, and why?

A brick-red precipitate of copper(I) oxide (Cu 2 O) forms and the solution changes from blue to colourless. The blue Cu 2+ ions act as an oxidising agent, oxidising the aldehyde to a carboxylic acid while being reduced to Cu + ions. A ketone gives no reaction and the solution remains blue.

A LevelChemistryEdexcelFlashcards7. Advanced Organic ChemistryOrganic Chemistry II: Carbonyl Chemistry

Organic Chemistry II: Carbonyl Chemistry (Edexcel A Level Chemistry): Flashcards

Exam code: 9CHO

1/17

0Still learning

Know0

FrontCarbonyl Compounds
Define aldehyde.

Was this flashcard helpful?

Cards in this collection (17)

Define aldehyde.
An aldehyde is a carbonyl compound in which the C=O group is positioned at the end of the carbon chain, with the general formula RCHO.
What is the 2,4-DNPH test?
The 2,4-DNPH test is a test for carbonyl compounds (aldehydes and ketones) in which 2,4-dinitrophenylhydrazine reacts with the C=O group in a condensation reaction to form an orange or yellow precipitate. The melting point of the precipitate identifies the specific carbonyl compound.
What is the position of the carbonyl group in an aldehyde compared to a ketone, and how does this affect their naming?
In an aldehyde, the C=O group is always at carbon-1 (the end of the chain), so the '1' is not included in the name (e.g. ethanal). In a ketone, the C=O group is always in the middle of the chain, so its position must be numbered (e.g. pentan-2-one).
How can acidified potassium dichromate(VI) be used to distinguish between an aldehyde and a ketone?
When warmed with acidified potassium dichromate(VI), an aldehyde is oxidised to a carboxylic acid and the solution changes from orange to green. A ketone is not oxidised under these conditions, so there is no colour change.
True or False?
Aldehydes and ketones can hydrogen bond with each other.
False.
Aldehydes and ketones have no O−H or N−H bonds, so there is no δ+ hydrogen available for hydrogen bonding between their own molecules. They experience permanent dipole-dipole interactions and London forces only.
True or False?
Warming a ketone with Tollens' reagent produces a silver mirror.
False.
Ketones cannot be oxidised by Tollens' reagent because they have no readily available hydrogen atom on the carbonyl carbon. Only aldehydes produce a silver mirror with Tollens' reagent.
Define ketone.
A ketone is a carbonyl compound in which the C=O group is positioned in the middle of the carbon chain, flanked by two alkyl groups, with the general formula RCOR'.
What is the silver mirror test (Tollens' test)?
The silver mirror test (Tollens' test) is a test using [Ag(NH₃)₂]⁺ (aq) to distinguish aldehydes from ketones. An aldehyde reduces the silver(I) complex ion to metallic silver, forming a silver mirror on the inside of the tube. A ketone gives no reaction.
Aldehydes and ketones have .......... boiling points than their equivalent alcohols because they cannot form .......... bonds with each other.
Aldehydes and ketones have lower boiling points than their equivalent alcohols because they cannot form hydrogen bonds with each other.
When reduced with LiAlH₄ in dry ether, an aldehyde forms a .......... alcohol and a ketone forms a .......... alcohol.
When reduced with LiAlH₄ in dry ether, an aldehyde forms a primary alcohol and a ketone forms a secondary alcohol.
What is the carbonyl group?
The carbonyl group is a C=O functional group found in aldehydes and ketones. The oxygen is more electronegative than carbon, creating a dipole with a δ+ carbon and a δ− oxygen.
What does a positive iodoform test indicate, and what is the positive result?
A positive iodoform test indicates the presence of a methyl ketone (CH₃CO− group) or ethanal. The positive result is a yellow precipitate of tri-iodomethane (CHI₃), formed when the compound is heated with an alkaline solution of iodine.
Why do smaller aldehydes and ketones dissolve in water, but larger ones do not?
Smaller aldehydes and ketones dissolve in water because their δ− oxygen atom uses lone pairs to form hydrogen bonds with the δ+ hydrogen of water molecules. Larger carbonyl compounds have longer hydrocarbon chains that disrupt water's hydrogen bonding without forming their own, so the energy cost of dissolving exceeds the energy gained.
Define nucleophilic addition.
Nucleophilic addition is a reaction in which a nucleophile attacks the δ+ carbon of a polarised C=O group, forming a new bond and adding across the double bond to give a single-bonded product.
True or False?
The simplest ketone is propan-2-one.
True.
Propan-2-one (CH₃COCH₃) is the simplest ketone because a ketone requires an alkyl group on each side of the carbonyl carbon, which means a minimum of three carbon atoms.
True or False?
The 2,4-DNPH test gives a positive result with carboxylic acids.
False.
The 2,4-DNPH test is selective for aldehydes and ketones. Carboxylic acids and esters also contain C=O groups but do not react with 2,4-DNPH — they do not possess an aldehyde or ketone functional group.
What is observed when Fehling's solution is warmed with an aldehyde, and why?
A brick-red precipitate of copper(I) oxide (Cu₂O) forms and the solution changes from blue to colourless. The blue Cu²⁺ ions act as an oxidising agent, oxidising the aldehyde to a carboxylic acid while being reduced to Cu⁺ ions. A ketone gives no reaction and the solution remains blue.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Organic Chemistry II: ChiralityNext:Organic Chemistry II: Carboxylic Acids