AQA A Level Chemistry

Topic Questions

3.7 Organic Mechanisms

1a1 mark

Figure 1 shows the breaking of a covalent bond, where the more electronegative atom B has taken both electrons from the bond to form a negative ion.

Figure 11

Name this type of bond fission.

1b2 marks

Using single headed arrows, show the movement of electrons when a molecule of chlorine, Cl2, is exposed to UV light according the equation.

Cl2 → 2Cl

1c1 mark

Explain why a hydrogen ion, H+, can behave as an electrophile.

1d2 marks

Propene, CH3CHCH2, can undergo electrophilic addition with hydrogen bromide, HBr, to form 2-bromopropane.

Figure 2 shows a partly completed mechanism. Use curly double headed arrows to complete the mechanism.

Figure 2

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2a1 mark

There are three steps to the free radical substitution mechanism.

When ethane and chlorine react in the presence of UV light, chloroethane is produced.

Write the equation for the initiation step.

2b2 marks

Write two equations for the propagation steps for the reaction outlined in part (a).

2c1 mark

Write the equation using structural formulae for the termination reaction between two CH3CH2• free radicals.

2d4 marks

The chloroethane formed in part (a) can react with excess ammonia, NH3, to form ethylamine and a Cl- ion.

i)
Name the reaction mechanism.

ii)
Outline the reaction mechanism for the formation of ethylamine from chloroethane. 

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3a3 marks

2-iodopropane, CH3CHICH3, reacts with ethanol and sodium hydroxide, NaOH, to form but-2-ene, C4H8, sodium iodide, NaI, and water.

The first step of the mechanism is given in Figure 1.

Figure 1

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i)
Name the reaction mechanism for the reaction.

ii)
Complete the mechanism for the reaction.
3b2 marks

Give the products of the reaction in part (a) if aqueous sodium hydroxide is used instead of ethanolic sodium hydroxide.

3c3 marks

1-chloropropane, 2-chloropropane and 2-methyl-2-chloropropane are examples of primary, secondary and tertiary halogenoalkanes.

State whether the primary, secondary and tertiary halogenoalkanes will favour undergoing nucleophilic substitution, elimination or both types of reactions.

3d1 mark

Explain why an OH- ion can behave as a nucleophile in the reaction between aqueous sodium hydroxide and 2-iodobutane, CH3CHICH2CH3.

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4a1 mark

But-1-ene, CH2CHCH2CH3, will react with bromine to produce 1,2-dibromobutane, CH2BrCHBrCH2CH3. Draw the skeletal structure of 1,2-dibromobutane.

4b4 marks

Name and outline the mechanism for the reaction in part (a). The first arrow has been drawn for you in Figure 1.

Figure 1

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4c2 marks

If but-1-ene reacts with hydrogen bromide, HBr, a major and a minor product are both formed. Name the major and minor products of this reaction.

4d3 marks

Explain why major and minor products are produced during the reaction between but-1-ene and hydrogen bromide, HBr.

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5a3 marks

A reaction pathway is shown in Figure 1.

Figure 1

5

Give the reagents and conditions required for Reaction 2.

5b3 marks

The mechanism involved in Step 2 is nucleophilic substitution.

Outline the reaction mechanism.

5c1 mark

Name compound C shown in Figure 1 in part (a).

5d4 marks

The reagents and conditions for Reaction 1 in Figure 1 of part (a) are ethanolic potassium hydroxide and heat under reflux.

i)
Outline the elimination mechanism for Reaction 1.

ii)
Compound B is an alkene and can undergo addition polymerisation.
Draw the repeating unit for the polymer formed from Compound B.

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1a3 marks

A cyanide ion can act as a nucleophile in nucleophilic substitution reactions.

Nucleophilic substitution of a halogenoalkane with a cyanide ion is an effective way of increasing the length of a carbon chain.

i)
Draw the Lewis structure of the cyanide ion.

ii)

Refer to your diagram to explain why the cyanide ion can act as a nucleophile.

1b4 marks

Suitable conditions for the nucleophilic substitution of a halogenoalkane are heating under reflux with a solution of sodium or potassium cyanide in ethanol.

i)
Outline the mechanism when 2-bromo-2-methylpropane is placed in these conditions.

ii)
State the name of the product.
1c1 mark

Aqueous conditions are used instead of alcoholic conditions for the reaction outlined in part (b). Draw the structure for the product of this reaction. 

1d6 marks

The product of the reaction outlined in part (c) is heated under reflux with concentrated sulfuric acid.

i)
Name and outline the mechanism of this reaction.

ii)

Explain why this reaction does not require a high temperature.

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2a6 marks

Name and outline the mechanism for the reaction between 1-methylcyclohex-1-ene and hydrogen bromide, HBr. In your answer, draw the major product of the reaction.

2b3 marks

Explain why a major product and minor product are produced in the reaction outlined in part (a).

2c2 marks

Predict the skeletal structure of the alkenes that would react with a hydrogen halide to produce the following compounds in Figure 1.

Figure 1

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2d2 marks

Halogen molecules can react with alkenes to produce halogenoalkanes which contain two halogen atoms. The covalent bond in the halogen molecule is not polar. . Explain why halogen molecules can react with alkenes.

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3a6 marks

Outline the mechanism and give the reagents and conditions for the reaction shown in Figure 1.

In your answer include the name and conditions required for the mechanism.

Figure 1

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3b2 marks

Explain how the conditions of this mechanism could be altered to produce a high yield of trichloromethyl benzene.

3c2 marks

In a separate reaction involving similar conditions as part (a) tetrachloromethane was produced from trichloromethane. Outline both propagation steps for this reaction.

3d3 marks

Draw all possible products of mono-substituted halogenoalkanes when 2-methylbutane undergoes reaction with bromine in the same conditions asked for in part (a).

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4a3 marks

For the reaction profile outlined in Figure 1, state the mechanism or type of reaction for each step.

Figure 1

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4b4 marks

Outline the mechanism for the conversion of 1-bromopropane to Compound G. In your answer give the reagents and conditions for the reaction.

4c5 marks

2-bromobutane undergoes a reaction to produce an unsymmetrical alkene. Name and outline the mechanism for this reaction and give the reagents and conditions required.

4d5 marks

An alternative pathway to form butylamine is to react 1-bromobutane with ammonia.

i)
Outline the full mechanism for this reaction.

ii)
Explain why an excess of ammonia would be required.

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5a2 marks

During the conversion of of 2-methylbutan-2-ol to an alkene, the reaction requires sodium or potassium hydroxide.

Explain the role of the hydroxide ion in this reaction.

5b3 marks

2-methylbutan-2-ol can be produced from the reaction of 2-iodo-2-methylbutane. Explain why this reaction would be quicker than using 2-chloro-2-methylbutane.

5c4 marks

A reaction pathway is shown in Figure 1. Compound J reacts with bromine water to form a colourless solution.

Figure 1

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i)
Name compound J.

ii)
Outline the reaction mechanism for the conversion of compound J to compound Y
5d5 marks

Outline the mechanism for the conversion of compound X to compound J and give the reagents and conditions required.

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1a1 mark

The chemical reactions which organic compounds undergo can be shown using a step by step reaction mechanism. 

In these mechanisms, curly arrows are used. 

What does a curly arrow represent in these mechanisms?

1b7 marks

The mechanism for the reaction between methane and chlorine is not represented using the curly arrow model, but rather a series of equations to represent what is happening at each stage of the reaction.

i)
Name this reaction mechanism, when methane reacts with chlorine.

ii)

Outline the mechanism, including all steps, stating the necessary reagents and the type of bond fission which is taking place. Name the first two stages of the reaction.

1c1 mark

Write the overall equation for the reaction between chlorine and methane.

1d3 marks

Chlorine will react with alkenes as well as alkanes, but the same conditions are not needed for this reaction to take place.

Explain why alkenes will readily react with chlorine.

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2a4 marks

Alkenes will react readily with hydrogen halides, such as hydrogen bromide.

2-methylprop-1-ene will react with hydrogen bromide.

Suggest the mechanism for this reaction, showing the formation of the major product which is formed.

2b2 marks

Draw the skeletal formula of the minor product that would be formed during this reaction and give its IUPAC name.

2c1 mark

Name the type of mechanism taking place in part (a).

2d2 marks

Explain why the major and minor products formed from the reaction in part (a) are not formed in equal amounts.

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3a2 marks

Halogenoalkanes are a very useful group of organic compounds, and are often used in organic synthesis.

The organic compound, CH3CHClCH2OH reacts with potassium hydroxide to form a diol, if the reaction conditions are appropriate.

Draw the displayed formula of CH3CHClCH2OH and give its IUPAC name.

3b2 marks

Give the reagents and conditions necessary to convert CH3CHClCH2OH into a diol and draw the skeletal formula of the diol that would be formed during the reaction.

3c3 marks

In the reaction in part (b) where a diol is formed, the hydroxide ions behave as nucleophiles.

Explain why the hydroxide ions behave as nucleophiles in the reaction in part (b).

3d4 marks

Name and outline the mechanism which is taking place when CH3CHClCH2OH is converted into a diol using the reagents and conditions from part (b).

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4a3 marks

Figure 1 below shows possible products which can formed from different reactions of a halogenoalkane.

Figure 1

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Reaction 1 takes place with dilute sodium hydroxide solution.

Draw the displayed formula and give the IUPAC name of compound A.

Give the classification of the compound formed. 

4b3 marks

Compound B is part of the homologous series which has the general formula CnH2n.

Give the reagents and conditions necessary to produce compound B.

4c5 marks

Name and outline the reaction mechanism for the reaction stated in part (b), to show how a product which has the key functional group on the first carbon atom is formed.

4d3 marks

The product drawn in part (c) has an isomer which does not show stereoisomerism.

Draw the displayed and skeletal formula of this isomer and explain why stereoisomerism does not arise in this product.

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5a6 marks

The following alkene in Figure 1 will undergo a number of different chemical reactions, depending on the reagents and conditions which are used.

Figure 1

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Name and outline a mechanism which would convert the alkene shown in Figure 1 to 2-bromo-4-methylpentane.

5b6 marks

Name and outline the mechanism, including necessary reagents, used to convert the product formed from the reaction in part (a) into an amine.

5c2 marks

The halogenoalkane produced from the reaction in part (a) can be converted back into the alkene shown in Figure 1.

Name the reagent and a key condition which would be necessary to ensure that the yield of the alkene formed during this reaction is high.

5d4 marks

The alkene in Figure 1 in part (a) can also be reacted with concentrated sulfuric acid.

Draw the mechanism to show the product formed when this reaction takes place.

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61 mark

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