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A-level Chemistry > Module 6: Aromatic Chemistry V1 > Flashcards

Module 6: Aromatic Chemistry V1 Flashcards

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1
Q

What is the number of sigma bond in a benzene molecule?

A

12 ✓

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2
Q

Deduce the number of sigma bonds in the following molecule.

A

21 ✓

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3
Q

What is the number of sigma bond in a methylbenzene molecule?

A

15 ✓

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4
Q

Which statement(s) support(s) the delocalised model for the structure of benzene?
A All carbon–carbon bonds have the same length.
B The enthalpy change of hydrogenation of benzene is less exothermic than expected.
C Bromine reacts with benzene less readily than with cyclohexene.

A

A, B and C ✓

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5
Q

Over time, the Kekulé and delocalised models have been used to describe the bonding and structure of a benzene molecule.

Describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekulé model and the delocalised model of benzene.

A

Similarities:
Sideways overlap of p orbitals. ✓
p orbitals to give a π-bond above and below ring plane ✓
Difference:
Kekule has 3 π-bonds with localised electrons, which overlap in one direction ✓
Delocalised model has π ring system, where all p orbitals overlap in both directions ✓

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6
Q

Over time, the Kekulé and delocalised models have been used to describe the bonding and structure of a benzene molecule.
Draw labelled diagrams to describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekulé model and the delocalised model of benzene.

A
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7
Q

Experimental evidence led to the general acceptance of the delocalised model over the Kekulé model.

Describe three pieces of evidence to support the delocalised model of benzene.

A
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8
Q
A
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9
Q

Describe what is meant by an “arene”

A

hydrocarbon containing at least one benzene ring. ✓

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10
Q
A
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11
Q

Compare and constrast the delocalised model of benzene with kekule’s structure.

A

Both have sideways overlap of p-orbitals ✓

Both have π bond above and below ring ✓

Kekule’s structure has 3 π bonds are localised ✓
Where as in the delocalised model there is delocalised π ring ✓

In kekules structure there are 2 electrons in each π bond ✓

and in the delocalised model there 6 electrons in one π bond (system) ✓

In kekules model, there is overlap in one direction ✓

but in the decalocalised model there is overlap in both directions ✓

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12
Q

Name the following compounds.

A
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13
Q

Experimental evidence led to the general acceptance of the delocalised model over the Kekulé model.

Describe three pieces of evidence to support the delocalised model of benzene.

A

All carbon–carbon bonds have the same length. ✓

The enthalpy change of hydrogenation of benzene is less exothermic than expected. ✓

Bromine reacts with benzene less readily than with cyclohexene and does not readily decolourise bromine by addition. ✓

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14
Q

Alkenes and benzene both react with bromine but alkenes are much more reactive.
Explain the relative resistance to bromination of benzene compared with alkenes.

A

In alkenes, pi electrons are localised between two carbons, have a region of high electron density and can polarise and attract a Br2 molecule. ✓
Colour change orange to colourless.✓
Alkenes can react with halogens in electrophilic addition reactions.✓

In benzene, pi electrons are delocalised, have a low electron density and cannot polarise and attract a Br2 molecule.✓
No colour change orange to colourless.✓
Benzene reacts with halogen carrier catalyst in electrophilic substitution reactions.✓

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15
Q

1) Give the conditions for the reaction between benzene and bromine to form bromobenzene.

2) Write an equation for the generation of the electrophile.

3) Using curly arrows, draw a mechanism for this reaction.

4) Write an equation to show the regeneration of the catalyst

A
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16
Q

Give a use of bromobenzene and chlorobenzene

A

Bromobenzene is used in preparation of pharmaceuticals. ✓

Chlorobenzene is used as a solvent and in preparation in pesticides. ✓

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17
Q

Give a use of nitrobenzene

A

To prepare dyes, pharmaceuticals and explosives.

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18
Q

1) Give the conditions for the reaction between benzene and nitric acid to form nitrobenzene

2) Why is the temperature in 1) used.

3) Write an equation for the generation of the electrophile

3) Using curly arrows, draw a mechanism for this reaction

4) Write an equation to show the regeneration of the catalyst

A
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19
Q

1) Give the conditions for the reaction between benzene and bromomethane to form methylbenzene (toluene)

2) Write an equation for the generation of the electrophile

3) Using curly arrows, draw a mechanism for this reaction

4) Write an equation to show the regeneration of the catalyst

A
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20
Q

1) Give the conditions for the reaction between benzene and ethanoyl chloride to form phenylethanone

2) Write an equation for the generation of the electrophile

3) Using curly arrows, draw a mechanism for this reaction

4) Write an equation to show the regeneration of the catalyst

A
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21
Q

Give the reagents needed to react with benzene, in the presence of a a halogen carrier catalyst, to form the following compounds.

A
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22
Q

Give the reagents needed to react with benzene, in the presence of a a halogen carrier catalyst, to form the following compounds.

A
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23
Q

i) Write an equation for the reaction of benzene with 2-chlorobutane in the presence of a halogen carrier catalyst.

ii) Draw the curly arrow mechanism for this reaction. Include the generation of the electrophile and the regeneration of the catalyst.

A
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24
Q

Write an equation for the reaction of benzene with bromine in the presence of a halogen carrier catalyst.

A
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25
Q

Write an equation for the reaction of benzene with concentrated nitric acid in the presence of a concentrated sulfuric acid catalyst.

A
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26
Q
A
27
Q
A
28
Q
A
29
Q
A
30
Q
A
31
Q

Phenol is a weak acid. Write an equation to show the dissociation of phenol.

A
32
Q

State two uses of phenol.

A

Phenol is used as an antiseptic and in disinfectants. ✓

It is used in the synthesis of dyes and pharmaceuticals ✓

33
Q

Using a labelled diagram, show how phenol is soluble in water.

A
34
Q

Explain why phenol is a solid and benzene is a liquid at room temperature and pressure.

A

Phenol has hydrogen bonding between molecules. ✓
Benzene has induced dipole-dipole interactions between molecules. ✓
Hydrogen bonding is stronger and requires more energy to overcome. ✓

35
Q

Write an equation for the reaction between phenol and NaOH.
a) Using skeletal formula.

b) Using molecular formula.

A
36
Q

Write an equation for the reaction between phenol and K.

a) Using skeletal formula.

b) Using molecular formula.

A
37
Q

a) Showing structures clearly, write an equation to show the bromination of phenol

b) Using molecular formula, write an equation to show the bromination of phenol

c) A student conducts an experiment in the laboratory, state the observation they would make from the above reaction.

A
38
Q

Compare the reactivity of cyclohexene, benzene and phenol with bromine.

A

In cyclohexene, two π-electrons are localised between 2 carbon atoms ✓
There is a high electron density ✓
Can polarise and attract a bromine molecule ✓
Electrophilic addition with a colour change from orange to colourless ✓

In benzene, six π-electrons are delocalised between 6 carbon atoms ✓
There is a lower electron density than an alkene. ✓
Only weakly polarises a bromine molecule. A halogen carrier catalyst is required to generate the more powerful electrophile Br+ ✓
Electrophilic substitution with no colour change ✓

In Phenol, six π-electrons are delocalised between 6 carbon atoms. ✓
lone pair of electrons in a p-orbital on O are delocalised into the ring, activating it. ✓
There is a higher electron density than benzene. ✓
Polarises a bromine molecule and attracts it without the need for a halogen carrier. ✓
Electrophilic substitution with a colour change from orange to colourless and formation of a white precipitate of 2,4,6-tribromophenol ✓

39
Q

Which one of the following reacts with ethanoic acid and with phenol?

A: Aqueous potassium hydroxide
B: Bromine
C: Calcium carbonate
D: Methanol and an acid catalyst

A

A: Aqueous potassium hydroxide. ✓

40
Q

Which chemical(s) can react with phenol?

Potassium hydroxide
Ethanoyl chloride
Nitric acid

A

All of them. ✓

41
Q

A student adds bromine water to a solution of phenol.

What would the student see during this reaction?

  1. Bromine water goes from orange to green.
  2. Bromine water goes from orange to colourless and a white precipitate is formed.
  3. There is no reaction.
  4. Bromine water goes from orange to colourless and the solution fizzes.
A
  1. Bromine water goes from orange to colourless and a white ✓
42
Q

Explain why phenol is nitrated more readily than benzene.

A
43
Q

Explain why phenol reacts with bromine more readily than benzene.

A
44
Q

Write an equation to show the nitration of phenol. Include an equation for eaceh product.

A
45
Q

State whether the following are deactivating/ activating and where they direct to.

A
46
Q

Write a series of reactions, using fully balanced equations, showing the synthesis of 4-chloronitrobenzene starting from benzene. Note: Chlorine is 2,4,6-directing.

A
47
Q
A
48
Q
A
49
Q

A chemist uses excess bromine to brominate phenylamine. Three molar equivalents of bromine react to form a single product. Suggest the structure of the product.

A
50
Q

A chemist nitrates bromobenzene. A mixture of mono-substituted products form. Suggest the structure of the products and name them. Br is 2,4-directing.

A
51
Q

The carboxyl group, COOH, is 3-directing. Write an equation for the nitration of benzoic acid.

A
52
Q

The methyl group has an activating effect on the benzene ring. When methylbenzene is brominated, a mixture of two di-substituted benzenes form. Isomer A is formed in 67% and isomer B in 33%. Suggest the structure of isomer A and isomer B and explain why a 50:50 mixture is not formed.

A
53
Q
A
54
Q

Write a series of reactions, using fully balanced equations, showing the synthesis of 4-chloronitrobenzene starting from benzene.

A
55
Q

Write a series of reactions, using fully balanced equations, showing the synthesis of 3-nitromethylbenzene starting from benzene.

A
56
Q

Write a series of reactions, using fully balanced equations, showing the synthesis of 2-nitromethylbenzene starting from benzene.

A
57
Q
A
58
Q

Phenol reacts with bromine

Which is the least likely product

A

C

59
Q

Compounds B and C, shown below, are unsaturated hydrocarbons containing nine carbon atoms.
Compound B reacts with chlorine at room temperature, but compound C requires the presence of a halogen carrier.
In both reactions, the organic compound reacts with chlorine in a 1:1 molar ratio.
Draw the structures of the organic product of each reaction.

A
60
Q
A

C. ✓

61
Q
A

A and C. ✓

62
Q

Toluene can be prepared from reacting benzene with a halogen carrier catalyst. Write an equation for this reaction.

A
63
Q

Ethanoyl chloride can react with benzene to form a ketone. Write an equation for this reaction.

A
64
Q

Complete the synthesis map to show the product of each reaction.

A

A-level Chemistry (15 decks)

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