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Chemistry OCR A-Level > Chapter 26 > Flashcards

Chapter 26 Flashcards

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1
Q

What carbonyl functional group do both aldhydes and ketones contain?

A

C=O

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2
Q

In aldehydes, where is the carbonyl functional group found?

A

At the end of a carbon chain

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3
Q

In its structural formula, what is the aldehyde group written as?

A

CHO

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4
Q

In its structural formula, what is the ketone group written as?

A

CO

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5
Q

What is the name of the simplest aldehyde?

A

methanal

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6
Q

What is the structure of the simplest aldehyde?

A

HCHO

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7
Q

What is the name of the simplest ketone?

A

propanone

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8
Q

What is the structure of the simplest ketone?

A

CH₃COCH₃

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9
Q

What is the common name for propanone?

A

acetone

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10
Q

What is the common name for methanal?

A

formaldehyde

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11
Q

What is formaldehyde used for?

A

To preserve biological specimens

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12
Q

How do you represent an oxidising agent?

A

[O]

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13
Q

What are aldehydes oxidised to?

A

Carboxylic acids

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14
Q

What are the conditions needed to oxidise aldehydes?

A

1) reflux
2) acidified dichromate(VI) ions, Cr₂O₇²⁻/H⁺
- -> sodium or potassium dichromate(VI), K₂Cr₂O₇
- -> dilute sulfuric acid, H₂SO₄

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15
Q

Can ketones be oxidised?

A

No

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16
Q

Can aldehydes be oxidised?

A

Yes

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17
Q

What influences the reactivity of aldehydes + ketones?

A

The nature of the carbon-oxygen double bond?

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18
Q

What is the carbon-hydrogen double bond made up of?

A

1) σ-bond

2) π-bond

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19
Q

Is the C=C double bond in alkenes polar or non-polar?

A

non-polar

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20
Q

Is the C=O double bond in carbonyl compounds polar or non-polar?

A

polar

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21
Q

Why is the C=O double bond polar?

A

1) oxygen is more electronegative than carbon
2) electron density in the double bond lies closer to the oxygen atom
3) carbon end of the bond is more positive
3) oxygen end of the bond more negative

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22
Q

What type of reactions do aldehydes + ketones undergo?

A

nucleophilic addition

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23
Q

What type of reactions do alkenes undergo?

A

electrophilic addition

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24
Q

What is a nucleophile?

A

An atom (or group of atoms) which is attracted to an electron-defficient centre or atom, where it donates a pair of electrons to form a new covalent bond

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25
Q

What is a σ-bond?

A

A bond formed by the overlap of one orbital from each bonding atom, consisting of two electrons and with the electron density centred around a line directly between the nuclei of the two atoms

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26
Q

What is a π-bond?

A

A bond formed above and below the plane of the carbon and oxygen atoms, formed by the sideways overlap of p-orbitals

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27
Q

What is the reducing agent used to reduce aldehydes and ketones to alcohols?

A

sodium tetrahydridoborate(III), NaBH₄

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28
Q

What type of alcohols are aldehydes reduced to?

A

Primary alcohols

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29
Q

How do you represent the reducing agent in the reduction of organic compounds?

A

[H]

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30
Q

What type of alcohols are ketones reduced to?

A

Secondary alcohols

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31
Q

What type of reaction is carbonyl compounds with HCN?

A

addition reaction

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32
Q

What two substances are used to provide hydrogen cyanide in reactions?

A

1) sodium cyanide

2) sulfuric acid

33
Q

Why can you not safely use hydrogen cyanide in an open laboratory?

A

It is an extremely poisonous liquid

34
Q

Why is the reaction of carbonyl compounds with HCN very useful?

A

It provides a means of increasing the length of the carbon chain

35
Q

What are the two functional groups formed from the reaction of an aldehyde with hydrogen cyanide?

A

1) hydroxyl group, -OH

2) nitrile group, C≡N

36
Q

What does an addition to carbonyl groups usually consist of?

A

1) nucleophilic attack on the carbonyl group to form a negatively charged intermediate
2) protonation of the intermediate to form an alcohol

37
Q

What is the nucleophile in NaBH₄?

A

the hydride ion, :H⁻

38
Q

What is the mechanism for the reaction of a carbonyl compound with NaBH₄?

A

1) lone pair of e- from hydride ion, :H⁻ attracted + donated to 𝛿+ C-atom in aldehyde/ketone C=O double bond
2) dative covalent bond formed between hydride ion and C-atom of C=O double bond
3) π-bond in C=O double bond breaks by heterolytic fission, forming negatively charged intermediate
4) O-atom of intermediate donates lone pair of e- to H-atom in water molecule. Intermediate has been protonated to form alcohol

39
Q

What is the mechanism for the reaction of a carbonyl compound with NaCN/H⁺?

A

1) lone pair of e- from cyanide ion, :CN⁻ attracted + donated to 𝛿+ C-atom in aldehyde/ketone C=O double bond –> dative covalent bond forms
2) π-bond in C=O double bond breaks by heterolytic fission, forming negatively charged intermediate
3) intermediate protonated by donating lone pair of e- to hydrogen ion, to form product
4) product is hydroxynitrile

40
Q

What is used to detect the presence of the carbonyl functional group in both aldehydes + ketones?

A

2,4-dinitrophenylhydrazine (2,4-DNP)

41
Q

What is produced when a carbonyl group is present in 2,4-DNP?

A

a yellow/orange precipitate

42
Q

What is 2,4-DNP usually dissolved in?

A

methanol + sulfuric acid

43
Q

Why is 2,4-DNP very hazardous?

A

Friction or a sudden blow can cause it to explode

44
Q

How do you carry out the test for the carbonyl group in aldehydes + ketones?

A

1) add 5cm depth 2,4-DNP to clean test tube
2) use dropping pipette to add 3 drops of unknown compound + leave to stand
3) if no crystals form, add few drops of sulfuric acid
4) yellow/orange precipitate = aldehyde/ketone

45
Q

What is used to detect the presence of the carbonyl functional group in aldehydes?

A

Tollens’ reagent

46
Q

What is produced when a carbonyl group is present in Tollens’ reagent?

A

A silver mirror

47
Q

How do you carry out the test for the carbonyl group in aldehydes?

A

1) pour 2cm depth of unknown solution into clean test tube
2) add equal volume of freshly prepared Tollens’ reagent
3) leave test tube to stand in beaker of warm water (around 50°) for 10-15 mins + observe whether a silver mirror is formed

48
Q

How do you identify an aldehyde or ketone by melting point?

A

1) filter impure yellow/orange solid to separate solid precipitate from solution
2) recrystallise solid to produce pure sample of crystals
3) measure + record melting point of purified carbonyl compound
4) compare melting point to database/data table of melting points to identify original carbonyl compound

49
Q

What is a carboxylic acid?

A

An organic acid which contains the carboxyl functional group

50
Q

What does the carboxyl functional group contain?

A

1) carbonyl group

2) hydroxyl group

51
Q

Why can carboxylic acids form hydrogen bonds with water molecules?

A

The C=O and O-H bonds in carboxylic acids are polar

52
Q

What is the maximum number of carbon atoms a carboxylic acid can have to be soluble in water

A

4

53
Q

What happens to the solubility as the number of carbon atoms in carboxylic acids increase?

A

Solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule

54
Q

What are dicarboxylic acids?

A

Acids with two polar carboxyl groups to form hydrogen bonds

55
Q

Are carboxylic acids strong or weak acids?

A

Weak acids

56
Q

Do carboxylic acids fully or partially dissociate in water?

A

Partially

57
Q

What type of reactions do carboxylic acids take place in?

A

1) redox reactions with metals

2) neutralisation reactions with metals

58
Q

What do carboxylic acids react with metals in a redox reaction to form?

A

hydrogen gas + carboxylate salt

59
Q

What do carboxylic acids react with metal oxides in a neutralisation reaction to form?

A

salt + water

60
Q

What do carboxylic acids react with alkalis in a neutralisation reaction to form?

A

salt + water

61
Q

What do carboxylic acids react with carbonates in a neutralisation reaction to form?

A

salt + carbon dioxide + water

62
Q

How do you test for the carboxyl group?

A

Neutralise carboxylic acids with carbonates as carboxylic acids are the only common organic compounds sufficiently acidic to react with carbonates

63
Q

What is a derivative of a carboxylic acid?

A

A compound that can be hydrolysed to form the parent carboxylic acid

64
Q

How do you name an acyl chloride?

A

Remove the -oic acid suffix from the parent carboxylic acid and replace with -oyl chloride

65
Q

How is an acid anhydride formed?

A

By the removal of water from two carboxylic acid molecules

66
Q

What is esterification?

A

The reaction of an alcohol with a carboxylic acid to form an ester

67
Q

What can esters be hydrolysed by?

A

1) aqueous acid

2) aqueous alkali

68
Q

What is hydrolysis?

A

the chemical breakdown of a compound in the presence of water or in aqueous solution

69
Q

How do you carry out acid hydrolysis?

A

heat ester under reflux with dilute aqueous acid

70
Q

What happens in acid hydrolysis?

A

ester is broken down by water, with acid acting as catalyst

71
Q

How do you carry out alkaline hydrolysis?

A

heat ester under reflux with aqueous hydroxide ions

72
Q

How do you prepare acyl chlorides?

A

react the parent carboxylic acid with thionyl chloride, SOCl₂

73
Q

What happens when water is added to an acyl chloride?

A

1) dense steamy hydrogen chloride fumes

2) carboxylic acid is formed

74
Q

How can ammonia and amines act as nucleophiles?

A

by donating the lone pair of electrons on the nitrogen atom to an electron-deficient species

75
Q

What happens when ammonia/amine is added to an acyl chloride?

A

forms an amide

76
Q

ammonia + acyl chloride –>

A

primary amine

77
Q

primary amine + acyl chloride –>

A

secondary amide

78
Q

Are acid anhydrides more or less reactive than acyl chlorides?

A

less

Chemistry OCR A-Level (28 decks)

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