Organic Mechanisms (AQA A Level Chemistry): Exam Questions

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?

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.

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

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.

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.

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

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

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

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.

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.

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).

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

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

Figure 1

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. 

Compound B is part of the homologous series which has the general formula C_nH_2n.

Give the reagents and conditions necessary to produce compound B.

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.

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.

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

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

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

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.

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.

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.

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.

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

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.

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.

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

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

Figure 1

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.

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

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

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

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

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

Figure 1

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

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.

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.

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.

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.

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

Figure 1

i) Name compound J.

ii) Outline the reaction mechanism for the conversion of compound J to compound Y. 

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