Aromatic Compounds | OCR A-Level Chemistry A (H432)

Aromatic Compounds

65 questions
6 subtopics
Module 6: Organic chemistry and analysis
Component 02 and Component 03

Benzene's delocalised structure and the evidence for it, electrophilic substitution and the directing effects of substituents, and phenol, which reacts far more readily than benzene and shows why..

It covers the delocalised model of benzene and the evidence for it, nitration, halogenation and Friedel-Crafts reactions of benzene, the reactions of phenol, and directing effects, electrophilic substitution and directing effects, phenol: acidity, bromination and nitration and why phenol is more reactive than benzene, and planning a synthesis.

Sample questions from Aromatic Compounds

Answer each one closed book first, then open the answer.

The delocalised model of benzene and the evidence for it

What type of system is formed when the p-orbitals in benzene overlap, and how is the electron density distributed?

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A delocalised π-system is formed, with electron density distributed equally around the ring.
The delocalised model of benzene and the evidence for it

How does the enthalpy change of hydrogenation of benzene provide evidence for delocalisation?

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The enthalpy change of hydrogenation is less exothermic than expected for a structure with three isolated double bonds.
Nitration, halogenation and Friedel-Crafts reactions of benzene

What reagents are used in a Friedel-Crafts reaction?

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A haloalkane or acyl chloride in the presence of a halogen carrier.
Nitration, halogenation and Friedel-Crafts reactions of benzene

In the nitration mechanism, what species acts as the electrophile?

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The nitronium ion (NO₂⁺).
The reactions of phenol, and directing effects

Does phenol require a catalyst to react with bromine water?

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No, phenol reacts with bromine water without a catalyst.
The reactions of phenol, and directing effects

If a benzene ring has an electron-donating substituent attached, at which positions would an incoming electrophile preferentially attack?

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Positions 2 and 4 (ortho and para positions).
Electrophilic substitution and directing effects

To which positions do electron-donating groups direct incoming electrophiles on a benzene ring?

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The 2, 4, and 6 positions (ortho and para positions)
Electrophilic substitution and directing effects

When planning a multi-step synthesis of a disubstituted benzene compound, what must be considered to obtain the desired isomer?

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The order of substitution reactions must be considered to exploit directing effects

The 6 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
The delocalised model of benzene and the evidence for it	Recall questions on the Kekulé and delocalised models, the overlapping p-orbitals, and the bond length and hydrogenation enthalpy evidence.	8
Nitration, halogenation and Friedel-Crafts reactions of benzene	Recall questions on the reagents for each, the nitronium ion and the halogen carrier, and why benzene resists bromination where an alkene does not.	10
The reactions of phenol, and directing effects	Recall questions on phenol with sodium hydroxide, with carbonates and with bromine water, and on which positions electron-donating and electron-withdrawing groups direct to.	10
Electrophilic substitution and directing effects	Recall questions on why substitution is favoured over addition, and on planning the order of steps in a disubstituted synthesis from the directing effects.	13
Phenol: acidity, bromination and nitration	Recall questions on the neutralisation with sodium hydroxide, distinguishing phenol from a carboxylic acid, and the mild conditions its bromination and nitration need.	11
Why phenol is more reactive than benzene, and planning a synthesis	Recall questions on the oxygen lone pair donated into the ring, its effect on electron density, and using directing effects to sequence a multi-step synthesis.	13

Aromatic Compounds is 65 of the 1,913 questions in the guide.Get the guide, £8

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.