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A Level Organic Chemistry > Chapter 26 - Carbonyls and Carboxylic Acids > Flashcards

Chapter 26 - Carbonyls and Carboxylic Acids Flashcards

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1
Q

What are carbonyl compunds ?

A

Compounds that contain a carbonyl functional group, C=O.

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2
Q

Nomenclature for aldehydes?

A

Aldehydes have the suffix -al. As the C=O bond is always at the end of the carbon chain, there is no need for a number. A unbranched chain of 5 carbons, with an C=O bond at the end would be pentanal.

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3
Q

Nomenclature for ketones?

A

The suffix is -one. For ketones with five or more carbons, you have to say which carbon the function group is on. For an unbranched 5 carbon chain, with the C=O bond on the second carbon, the name would be pentan-2-one.

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4
Q

What do aldehydes oxidise to become?

A

Carboxylic acids

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5
Q

Why are aldehydes easily oxidised?

A

There’s a hydrogen attached to the carbonyl group.

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6
Q

What are the conditions to oxidise aldehydes?

A

You need to reflux them with acidified potassium dichromate.

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7
Q

Why are ketones not easily oxidised?

A

You would have to break a carbon-carbon bond

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8
Q

What does the reduction of an aldehyde form?

A

A primary alcohol.

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9
Q

What does the reduction of a ketone form?

A

A secondary alcohol.

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10
Q

What is the reducing agent used to turn ketones/aldehydes back into alcohols?

A

NaBH4- sodium tetrahybridoborate (III)

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11
Q

What is the mechanism for the reduction of carbonyl compunds?

A

Nucleophillic addition

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12
Q

How does Nucleophillic addition reactions work?

A

1) oxygen has negative dipole and carbon has positive dipole.

2) an arrow from the lone pair on the H- ion to the carbon atom. Then arrow from double bond to oxygen atom.

3) H atom now covalently bonded to carbon atom and oxygen has lone pair of electrons and a minus charge.

4) arrow from lone pair on oxygen to H atom on water molecules. Then from the bond to the oxygen atom in the water molecule. Make sure to draw dipoles on water molecules.

5) this forms an alcohol and a OH- ion.

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13
Q

What does the reaction of carbonyl compounds with hydrogen cyanide produce?

A

Hydroxynitriles

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14
Q

How does Nucleophillic addition work with hydrogen cyanide?

A

1) hydrogen cyanide dissociates in water to produce H+ ions and CN- ions.

2) arrow from CN- ion to carbon atom. Arrow from double bond to oxygen atom.

3) CN bonded to carbon and Oxygen Atom now has a lone pair of electrons. Arrow from lone pair to H+ ion

4) this forms a hydroxyl group and a hydroxynitrile is produced.

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15
Q

What is used instead of hydrogen cyanide in labratories?

A

Sodium cyanide and Sulfuric acid.

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16
Q

What reagent is used to identify is a carbonyl group is present?

A

Brady’s reagent - 2,4- dinitrophenylhydrazine

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17
Q

What will you see if a carbonyl group is present when Brady’s reagent is added?

A

A bright orange precipitate forms. This only happens with ketones and aldehydes, not with COOH groups .

18
Q

How to identify the carbonyl compound from the orange precipitate formed from Brady’s reagent?

A

1) the precipitate is filtered and then recrystallised to form pure crystals.

2) then measure the melting point and compare to the literature values.

19
Q

How to distinguish between an aldehyde and a ketone?

A

Tollen’s reagent

20
Q

How does tollen’s reagent work + positive result?

A

Tollen’s reagent is a colourless solution of silver nitrate (AgNO3) dissolved in aqueous ammonia. It is heated in a test tube with an aldehyde. The aldehyde is oxidised to form a carboxylic acid. Then the silver ions in the Tollen’s reagent are reduced to produce a silver mirror.

Ag+ (aq). + e- ->. Ag(s)

21
Q

What are carboxylic acids?

A

Compounds with a -COOH functional group

22
Q

Why are carboxylic acids soluble?

A

Carboxylic acids are polar molecules, as there is a difference in electronegativity between the carbon and oxygen atoms. This allows carboxylic acids to form hydrogen bonds with water molecules.

23
Q

What is the dissociation of carboxylic acids?

A

As carboxylic acids are weak acids they dissociate into a carboxylate ion and H+. The H from the OH in the COOH is removed to form a H+ ion and a negative charge is left on the oxygen.

24
Q

Reaction of carboxylic acids and metals?

A

They react with metals to form a salt and hydrogen
Example : ethanoic acid + Mg -> magnesium ethanoate + H2

25
Q

Reaction of carboxylic acids with carbonates?

A

Carboxylic acids react with carbonates to form salt, carbon dioxide and water.

Example: ethanoic acid + sodium carbonate -> sodium ethanoate + H20 + CO2

26
Q

Reaction of carboxylic acid and metal oxide?

A

This is a neutralisation reaction forming water and a salt.

Example: ethanoic acid + magnesium oxide -> magnesium ethanoate + H2O

27
Q

What are acyl chlorides?

A

Acyl chlorides have the functional group COCl.

28
Q

General formula of acyl chlorides?

A

CnH2n-1OCl

29
Q

How to name acyl chlorides?

A

The names end with a -oyl chloride. So a five carbon chain with a COCl functional group at the end of the chain is called pentanoyl chloride.

30
Q

How to form acyl chlorides?

A

By reacting carboxylic acids with SOCl2 (thionyl chloride). This forms the acyl chloride, SO2 and HCl

31
Q

What is the reaction of acyl chloride with water?

A

Acyl chlorides react vigorously with cold water, producing a carboxylic acid.

Example: ethanoyl chloride + H2O -> ethanoic acid + HCl

32
Q

Reaction of acyl chlorides with alcohols?

A

Acyl chlorides react vigorously with alcohols at room temperature, producing an ester and HCl.

Example: ethanoyl chloride + Methanol -> methyl ethanoate + HCl

33
Q

Reaction of acyl chlorides with ammonia?

A

Acyl chlorides react violently with ammonia at room temperature, producing a primary amide.

Example: ethanoyl chloride + NH3 -> ethanamide + HCl

34
Q

Reaction of acyl chlorides with amines?

A

Acyl chlorides react violently with amines at room temperature to form a secondary amide + HCl

Example: ethanoyl chloride + methylamine -> N-methylethanamide + HCl

35
Q

Reaction of acyl chlorides with phenol?

A

Acyl chlorides react slowly with phenol at room temperature to form an ester +HCl.

Example: ethanoyl chloride + phenol -> phenylethanoate + HCl

36
Q

What is an ester?

A

An ester is formed from a carboxylic acid and an alcohol group

37
Q

How do you name esters?

A

The first half of the name comes from the alcohol. The second part comes from the carboxylic acid group. So methanoic acid + ethanol would form ethyl methanoate.

38
Q

Reaction of ethanoic acid and ethanol + conditions?

A

Produces ethyl ethanoate + water. The reaction is called esterificstion and requires an acid catalyst usually concentrated H2SO4. The reaction is reversible

39
Q

What is an acid anhydride?

A

An acid anhydride is produced from two identical carboxylic acid molecules. The OH from one carboxylic acid is removed and the H from another is removed to form water.

40
Q

How do acid anhydrides produce esters?

A

They are heated with alcohols to form esters and a Carboxylic acid which can be seperated by distillation.

41
Q

How does acid hydrolysis of esters work?

A

This splits the ester into a carboxylic acid and an alcohol. You have to heat the ester under reflux with a dilute acid, such as hydrochloric or Sulfuric.

42
Q

How does base hydrolysis of esters work?

A

You reflux the ester with a dilute alkali such as sodium hydroxide. When heated, OH- ions from the base react with the ester and you get a carboxylate ion and an alcohol

A Level Organic Chemistry (5 decks)

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