These questions are not relevant to AQA A-level Chemistry but are important for OCR A-level students.
For the following reagents, draw the skeletal formulae of the major organic product of the reactions. In each of the reactions, assume that only one substitution takes place.
a) Methylbenzene and concentrated nitric acid in the presence of a concentrated sulfuric acid catalyst.
Answer
Methyl group is 2,4-directing.
b) Chlorobenzene and chloroethane in the presence of aluminium chloride.
Answer
Chlorine is 2,4-directing.
c) Nitrobenzene and nitric acid in the presence of a sulfuric acid catalyst.
Answer
Nitro group is 3-directing.
d) Phenol and chlorine in the presence of aluminium chloride.
Answer
OH group is 2,4-directing.
e) Benzonitrile and bromine in the presence of iron bromide.
Answer
Nitrile group is 3-directing.
f) 1-phenylethanone and ethanoyl chloride in the presence of aluminium chloride.
Answer
Acyl group is 3-directing.
Methylbenzene reacts with excess concentrated nitric acid in the presence of sulfuric acid.
a) Assuming multiple substitutions take place, draw the skeletal formulae of the organic molecule that is formed.
Answer
b) Explain why this product is formed, rather than the minor product.
Answer
The methyl group is electron releasing and therefore stabilises the carbocation intermediate formed during the formation of 2-nitromethylbenzene or 4-nitromethylbenzene (2,4-directing).
c) Explain why methylbenzene reacts more quickly with nitric acid than benzene does.
Answer
The mechanism proceeds via a carbocation. The carbocation in the reaction with methylbenzene is a tertiary carbocation (or stabilized secondary), whereas in the reaction with benzene, the carbocation is secondary.
The intermediate is more stable due to experiencing a stronger positive inductive effect from the alkyl group.
Phenol reacts with chloromethane.
a) State the catalyst required for this reaction to take place.
Answer
Aluminium chloride (AlCl3)
b) Write the equation for the reaction that forms the electrophile.
Answer
CH3Cl + AlCl3 → CH3+ + AlCl4–
c) Draw the skeletal formula for the major product that forms during this reaction. Assume that multiple substitutions take place.
Answer
d) Outline the mechanism that occurs during the second substitution reaction that takes place.
Answer
OR
