Extending Carbon Chains (OCR A Level Chemistry A): Exam Questions

Ethylbenzene, C₆H₅CH₂CH₃, is an important chemical intermediate in the manufacture of polystyrene, pesticides, rubber, paint and inks.

The synthesis of ethylbenzene can occur via Friedel-Crafts alkylation using ethene, hydrogen chloride, benzene and an aluminium chloride, AlCl₃, catalyst. 

Name the mechanism for the reaction of ethene and hydrogen chloride.

Write an equation for the subsequent formation of the carbocation that reacts with benzene to produce ethylbenzene.

Outline the mechanism for the reaction of benzene with the carbocation that was formed in part (a).

1-methylpropylbenzene, C₆H₅CH(CH₃)CH₂CH₃ is the major organic product formed when benzene and but-1-ene react together in the presence of aluminium bromide and hydrogen bromide. Write an equation showing the formation of the electrophile required for this reaction. 

Explain why a minor product of butyl benzene, C₆H₅CH₂CH₂CH₂CH₃, is produced in this reaction. 

Propanal reacts with potassium cyanide, followed by dilute acid, to form the hydroxynitrile CH₃CH₂CH(OH)CN.

Give the IUPAC name of CH₃CH₂CH(OH)CN. 

Name the mechanism for the reaction between potassium cyanide and propanal.

Propanone undergoes the same reaction with HCN as propanal to form a hydroxynitrile.

Outline the mechanism for the reaction.

Suggest why carbonyl compounds are likely to undergo nucleophilic attack. 

Benzene is a useful in the production of pharmaceuticals, however due to the stability of the benzene ring it is fairly unreactive with electrophiles. Instead stronger electrophiles can be made by using a halogen carrier such as aluminium chloride, AlCl₃ with ethanoyl chloride. 

Give an equation to show the generation of an electrophile using aluminium chloride.

Outline the mechanism for the reaction of the electrophile with benzene to produce 1-phenylethanone.

Outline the mechanism for the reaction of the ethanoyl chloride with the catalyst to form the acylium ion needed for electrophilic substitution.

Aluminium chloride is used as the catalyst in the reaction between benzene and ethanoyl chloride. Explain how the catalyst reforms.

A reaction pathway to produce a carboxylate salt, Compound M, which contains three carbon atoms is shown below.

Bromoethane → Compound L → Compound M

Give the correct reagents to form compound L from bromoethane.

Name and outline the mechanism for the formation of Compound L from bromoethane.

State the reagents required for the formation of Compound M from Compound L and give an equation for the reaction.

A chemist reacted Compound L with hydrogen gas in the presence of a nickel catalyst. Name and draw the structure of the compound produced.

Compounds A and B can be formed in the reaction scheme shown in Figure 1.

Compound B is a primary amine with the molecular formula C₇H₁₇N

Figure 1

Explain how compounds A and B can be formed. In you answer include required reaction conditions and regents as well as the structure of compounds A and B. 

State the IUPAC names for compounds A and B.

Using curly arrows, describe the mechanism for the reaction 1.

Compound A can be hydrolysed via two methods. 

Explain how compound A can be hydrolysed. In your answer include relevant equations.

Propylamine, shown in Figure 1, can be synthesised from ethene.

Figure 1

A student suggests that ethene should be reacted with hydrogen cyanide to produce propylamine. 

Figure 2 shows the outline of a reaction scheme to convert ethene into propylamine.

Figure 2

Ethene  Compound A  Compound B  Propylamine

Identify which step of the reaction scheme could use the student’s suggestion of hydrogen cyanide. Justify your answer.

Draw the skeletal structure of compound A, from part a), and state the reagents required for its formation.

The final step of the reaction scheme will form the desired amine.

i) State the IUPAC name of compound B.

[1]

ii) Identify the type of reaction that compound B undergoes to form propylamine. Justify your answer.

[1]

Benzene undergoes a substitution reaction to form compounds X and Y. This is shown in Figure 1.

Figure 1

State the formulas of the reagents required for reaction 1.

Propene will react with benzene in the presence of aluminium chloride and hydrogen chloride to form compound Y. 

Using curly arrows, describe the mechanism which will generate the electrophile.

Using curly arrows, describe the mechanism for the formation of compound Y. In your answer show how AlCl₃ is regenerated. 

State the type of reaction that occurs in both reactions in part a).

Lactic acid, CH₃CH(OH)COOH, can be formed from compound X in three steps as shown below.

Compound X  Ethanal  Compound Y  Lactic acid

Compound X undergoes oxidation to form ethanal. 

i) State the IUPAC name for compound X.

[1]

ii) Draw the apparatus which is required for step 1.

[3]

Using curly arrows, describe the mechanism for step 2.

State the reagents required for step 3.