AQA A Level Chemistry

Topic Questions

3.7 Organic Mechanisms

11 mark

Which reaction occurs when ethane and chlorine are mixed in the presence of sunlight?

  • A free-radical substitution with hydrogen produced

  • A free-radical substitution with hydrogen chloride produced

  • A free-radical substitution with no gas produced

  • A nucleophilic substitution with hydrogen chloride produced

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21 mark

High-energy irradiation in the stratosphere produces radicals from chlorofluoroalkanes, commonly known as CFCs.

Which radical could result from this irradiation of CHFClCF2Cl ?

  • CHFClCFCl

  • CHClCF2Cl

  • CHFCF2Cl

  • CFClCF2Cl

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31 mark

Bromomethane, CH3Br, is used as a fumigant to destroy insect pests in grain that is to be stored. It can be made by reacting methanol with hydrogen bromide.

CH3OH  +  HBr  →  CH3Br  + H2O

What type of reaction is this?

  • Condensation

  • Electrophilic substitution

  • Free radical substitution

  • Nucleophilic substitution

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41 mark

What type of reaction makes ethylamine from bromoethane?

  • Oxidation

  • Reduction

  • Nucleophilic substitution

  • Electrophilic substitution

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51 mark

The equation shows an organic reaction

CH3CH2CHClCH3  +  CN  →  CH3CH2CH(CH3)CN  +  Cl

What is the name for this type of reaction?

  • Nucleophilic substitution

  • Electrophilic substitution

  • Free radical substitution

  • Elimination

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61 mark

This molecule is responsible for the flavour of spearmint chewing gum.

q6-3-7-easy-mcq-organic-mechanisms

What is a true statement about the functional groups 1 or 2?

  • 1 will undergo electrophilic addition

  • 1 will undergo electrophilic substitution

  • 2 will undergo nucleophilic substitution

  • 2 will undergo electrophilic substitution

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71 mark

The decomposition of ozone contributes to formation of a hole in the stratosphere. Two equations which represent part of the process are:

Cl + O3 → ClO + O2 and ClO + O3 → 2O2 + Cl

Which statement is correct about the decomposition of ozone?

  • One chlorine radical is responsible for decomposing one ozone molecule

  • Chlorine radicals are catalytic in the process

  • Two ozone molecules change into two oxygen molecules

  • Chlorine radicals have a full shell of electrons

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81 mark

The addition of hydrogen bromide, HBr, to pent-2-ene, CH3CH2CH2CH=CH2 , produces

  • 1-bromopentane

  • 2-bromopentane

  • 1,2-dibromopentane

  • A mixture of 1-bromopentane and 2-bromopentane

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91 mark

In the reaction scheme shown,

q9-3-7-easy-mcq-organic-mechanisms

Which of the following statements is correct?

  • Product 1 is the major product

  • Product 2 is the major product

  • A 50:50 mixture of the two products is formed

  • The bromine acts as an electrophile

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101 mark

An incomplete mechanism for the reaction of concentrated sulfuric acid with butan-1-ol is shown below.

q10-3-7-easy-mcq-organic-mechanisms

Which of the following fragments in this mechanism is incorrect?

q10-2-3-7-easy-mcq-organic-mechanisms

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11 mark

The reaction sequence below shows a pair of reaction types.

q1-3-7-hard-mcq-organic-mechanisms

Which row in the table correctly shows the two reaction types?

 

reaction 1

reaction 2

A

nucleophilic addition

nucleophilic substitution

B

electrophilic addition

electrophilic substitution

C

nucleophilic addition

electrophilic substitution

D

electrophilic addition

nucleophilic substitution

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21 mark

Bromine will react with ethane in a free radical substitution reaction. Which reaction is not a valid termination step in the mechanism?

  • H• + Br• → HBr

  • Br•  + Br• → Br2

  • C2H5•  +  Br•  → C2H5Br

  • C2H5•  + C2H5•  → C4H10 

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31 mark

The chlorination of methane can produce multiple products.

What is the most likely proportion of these products in a reaction mixture?

  • CH3Cl  > CH2Cl2  > CH3CH3  > CCl4

  • CH3Cl  > CH3CH3 > CH2Cl2  > CCl4

  • CCl4 > CH3CH3 > CH2Cl2  > CH3Cl   

  • CH3Cl > CH2Cl2  > CCl4> CH3CH3 

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41 mark

Which of the following substances cannot be a product of nucleophilic substitution of 1-bromobutane?

  • Butan-1-ol

  • Pentanenitrile

  • But-1-ene

  • 1-aminobutane

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51 mark

1-bromopropane undergoes nucleophilic substitution with excess ammonia. A student has drawn the mechanism for the reaction, but has made an error in the diagram.

q5-1-3-7-hard-mcq-organic-mechanisms

The segment which contains the error is

q5-2-3-7-hard-mcq-organic-mechanisms

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61 mark

The mechanism for the reaction between hot potassium hydroxide in ethanol and chloroethane is shown below

q6-3-7-hard-mcq-organic-mechanisms

Which of the following statements is not correct?

  • The hydroxide ion acts as a base but not a nucleophile

  • The hydroxide ion acts as a nucleophile and a base

  • Ethanol could also be a product in the same reaction

  • The hydrogen atoms in the chloroethane are very slightly ẟ+

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71 mark

Chlorofluorocarbons (CFCs) from refrigerants, propellants and aerosols are known to be responsible for the destruction of the ozone layer in the stratosphere. 

One early CFC was trichlorofluoromethane, CCl3F.

Which step from a possible mechanism for the destruction of ozone is not likely?

  • CCl3 F→ CFCl2 + Cl

  • Cl + O3 → ClO + O2

  • CFCl2 + O2 → CFClO + ClO

  • ClO + O3 → 2O2+ Cl

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81 mark

How many positional isomers can be obtained by the reaction of concentrated sulfuric acid with 1,3-cyclohexadiene followed by the addition of water?

  • 1

  • 2

  • 3

  • 4

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91 mark

2-methylbuta-1,3-diene reacts with hydrogen bromide to give a number of products.

q9-3-7-hard-mcq-organic-mechanisms

What is the major product of this reaction?

  • CH2BrCH(CH3)CH2CH2Br

  • CH2BrCH(CH3)CHBrCH3

  • CH3C(CH3)BrCH2CH2Br

  • CH3C(CH3)BrCHBrCH3

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101 mark

The dehydration of alcohols is an elimination reaction, resulting in an alkene and water as the only products.

What is the correct structure of the intermediate species in the mechanism for the dehydration of butan-2-ol that leads to the formation of the alkene?

q10-3-7-hard-mcq-organic-mechanisms

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11 mark

What is the major product formed when compound Q is warmed with excess HBr?

q1-3-7-medium-mcq-organic-mechanisms

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21 mark

Ethene reacts with aqueous bromine to give two products, CH2BrCH2Br and CH2BrCH2OH.

Which statement about these products is correct?

  • both products are obtained in this reaction by electrophilic substitution

  • both products are obtained in this reaction by nucleophilic addition

  • both products can be hydrolysed to form the same organic compound

  • both products can form hydrogen bonds with water

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31 mark

In the presence of ultraviolet light, ethane and chlorine react to give a mixture of products.

Which compound could be present in the mixture of products?

  • CH3Cl

  • CH3CH2CH2CH3

  • CH3CH2CH2Cl

  • CH3CH2CH2CH2CH3

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41 mark

In the hydrolysis of bromoethane by aqueous sodium hydroxide, what is the nature of the attacking group and of the leaving group?

 

attacking group

leaving group

A

B

C

D

electrophile

electrophile

nucleophile

nucleophile

electrophile

nucleophile

nucleophile

electrophile

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51 mark

What statement is true about the mechanism of the reaction between aqueous sodium hydroxide and 1-bromobutane

  • attack by a nucleophile on a carbon atom with a partial positive charge

  • heterolytic bond fission and attack by a nucleophile on a carbocation

  • homolytic bond fission and attack by an electrophile on a carbanion

  • homolytic bond fission and attack by a nucleophile on a carbocation

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61 mark

The reaction mechanism between ethanol and hot concentrated phosphoric acid is classified as

  • nucleophilic substitution

  • free radical substitution

  • elimination

  • electrophilic addition

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71 mark

Which equation represents a correct propagation step in the free radical substitution reaction between ethane and chlorine?

  • C2H6 + Cl → C2H5Cl + H

  • C2H6 + H → C2H5 + HCl

  • C2H5 + Cl2  → C2H5Cl + Cl 

  • C2H5 + Cl → C2H5Cl 

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81 mark

The following mechanism is missing the arrows showing the movement of electron pairs.

q8-3-7-medium-mcq-organic-mechanisms

Which of the following descriptions of the missing arrows is correct?

 


 

1st arrow

2nd arrow

3rd arrow

Curly arrow from lone pair of :OH- to the H of the C-H bond

Curly arrow from the C-H bond to the C-C bond

Curly arrow from the I to the C-I bond

A

B

C

D

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91 mark

A student has drawn a mechanism to show electrophilic addition. In which part of the mechanism did the student make a mistake?

q9-3-7-medium-mcq-organic-mechanisms

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101 mark

The following diagram shows a nucleophilic substitution mechanism, but only one of the arrows is correctly drawn

q10-3-7-medium-mcq-organic-mechanisms

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