Aromatic Hydrocarbons

Chemistry, HSSC-Punjab Second Year. This chapter is split into 37 topics and has 854 practice questions. The topics covered are listed below, followed by 10 free sample questions from the chapter.

Topics in this chapter

1. Ortho-Para Directing Groups 24 questions
2. Halogenation of Benzene 25 questions
3. Friedel-Crafts Acylation 22 questions
4. Bond Lengths in Benzene and Table 20.1 24 questions
5. Friedel-Crafts Alkylation 25 questions
6. Mechanism of Bromination and Chlorination of Benzene 22 questions
7. Sulphonation and Other Electrophiles 22 questions
8. KMnO4 Test for Benzylic Hydrogen 22 questions
9. General Mechanism of Electrophilic Aromatic Substitution 23 questions
10. Geometry of Benzene 23 questions
11. Predicting Products of Nitration and Halogenation 20 questions
12. Nitration of Benzene Reagents and Electrophile 21 questions
13. Kekule Structure of Benzene 20 questions
14. Exercise Style Questions on Aromatic Reactions 23 questions
15. Aromatic Compounds and Arenes 23 questions
16. Delocalisation of Pi Electrons in Benzene 21 questions
17. Side Chain Oxidation of Alkylbenzenes 29 questions
18. Polycyclic Aromatic Hydrocarbons 23 questions
19. Addition of Halogens to Benzene 22 questions
20. Reactivity of Benzene Compared with Alkanes and Alkenes 22 questions
21. Combustion of Benzene and Arenes 28 questions
22. Nitration Conditions and Calculations 20 questions
23. Naming Substituted Arenes 22 questions
24. Resonance Energy and Relative Stability 21 questions
25. Sigma Complex Arenium Ion 21 questions
26. Molar Masses of Benzene Derivatives 24 questions
27. Hydrogenation of Benzene 21 questions
28. Heats of Hydrogenation of Cyclohexenes 30 questions
29. Atom Economy and Percentage Yield in Aromatic Reactions 21 questions
30. Names of Monosubstituted Benzenes 25 questions
31. Priority Rules for Disubstituted Benzenes 24 questions
32. Synthetic Routes from Benzene 22 questions
33. Meta Directing Groups 23 questions
34. Friedel-Crafts Products and Comparisons 23 questions
35. Activation of the Ring by Phenol and Alkyl Groups 21 questions
36. Ortho Meta and Para Positions 25 questions
37. Atomic Orbital Structure of Benzene 27 questions

Sample questions: Aromatic Hydrocarbons

10 sample questions with the correct answer and an explanation. Try to answer each one before reading the explanation.

Q1. Which feature of vanillin makes it an aromatic compound?

• A. It contains a hydroxyl group
• B. It contains a carbonyl group
• C. It has a pleasant smell and sweet taste
• D. It contains a benzene ring(correct answer)

Answer: D.Aromatic character depends on the benzene ring in the structure; vanillin has a benzene ring carrying OH, OCH₃ and CHO groups. The smell, carbonyl or hydroxyl group alone do not make a compound aromatic.

Q2. The Kekulé structure explained many properties of benzene, but there were problems with it. The main drawback was that it

• A. did not fully explain the physical and chemical properties of benzene(correct answer)
• B. could not show the number of carbon atoms in the ring
• C. predicted that benzene would not form any substitution products
• D. gave the wrong molecular formula for benzene

Answer: A.The textbook states that Kekulé's structure explained many properties but did not fully explain the physical and chemical properties of benzene (equal bond lengths, stability, substitution rather than addition).

Q3. A benzene ring bears COOH on C-1 and OH in the meta (1,3) position. Its IUPAC name is

• A. 4-hydroxybenzoic acid
• B. 3-hydroxybenzoic acid(correct answer)
• C. 2-hydroxybenzoic acid
• D. 3-carboxyphenol

Answer: B.COOH has the higher priority, so the compound is named as a benzoic acid with the hydroxy prefix at C-3: 3-hydroxybenzoic acid. Wrong locants or a prefix name for the higher-priority group are incorrect.

Q4. A benzene ring bears COOH on C-1 and Cl in the para (1,4) position. Its IUPAC name is

• A. 3-chlorobenzoic acid
• B. 4-chlorobenzoic acid(correct answer)
• C. 4-carboxychlorobenzene
• D. 2-chlorobenzoic acid

Answer: B.COOH has the higher priority, so the compound is named as a benzoic acid with the chloro prefix at C-4: 4-chlorobenzoic acid. Wrong locants or a prefix name for the higher-priority group are incorrect.

Q5. A benzene ring bears COOH on C-1 and CH₃ in the ortho (1,2) position. Its IUPAC name is

• A. 3-methylbenzoic acid
• B. 2-methylbenzoic acid(correct answer)
• C. 4-methylbenzoic acid
• D. 2-carboxymethylbenzene

Answer: B.COOH has the higher priority, so the compound is named as a benzoic acid with the methyl prefix at C-2: 2-methylbenzoic acid. Wrong locants or a prefix name for the higher-priority group are incorrect.

Q6. A benzene ring bears CHO on C-1 and OH in the ortho (1,2) position. Its IUPAC name is

• A. 1-hydroxy-2-formylbenzene
• B. 3-hydroxybenzaldehyde
• C. 2-hydroxybenzaldehyde(correct answer)
• D. 4-hydroxybenzaldehyde

Answer: C.CHO has the higher priority, so the compound is named as a benzaldehyde with the hydroxy prefix at C-2: 2-hydroxybenzaldehyde. Wrong locants or a prefix name for the higher-priority group are incorrect.

Q7. A benzene ring bears CHO on C-1 and Cl in the para (1,4) position. Its IUPAC name is

• A. 1-chloro-4-formylbenzene
• B. 4-chlorobenzaldehyde(correct answer)
• C. 3-chlorobenzaldehyde
• D. 2-chlorobenzaldehyde

Answer: B.CHO has the higher priority, so the compound is named as a benzaldehyde with the chloro prefix at C-4: 4-chlorobenzaldehyde. Wrong locants or a prefix name for the higher-priority group are incorrect.

Q8. What is the major product(s) of the reaction of methylbenzene with Cl₂ and AlCl₃ in the absence of UV light?

• A. 1,3-dichlorobenzene and methane as products
• B. (chloromethyl)benzene formed on the side chain
• C. 2-chloromethylbenzene and 4-chloromethylbenzene(correct answer)
• D. 3-chloromethylbenzene as the only major product

Answer: C.2-chloromethylbenzene and 4-chloromethylbenzene is expected from the directing effect of the group on the ring (or addition under UV); the other answers apply the wrong directing effect or conditions.

Q9. What is the major product(s) of the reaction of chlorobenzene with Br₂ and AlBr₃?

• A. bromobenzene and chlorine gas
• B. 1,2-dichlorobenzene and Br₂
• C. 1-bromo-3-chlorobenzene as the main product
• D. 1-bromo-2-chlorobenzene and 1-bromo-4-chlorobenzene(correct answer)

Answer: D.1-bromo-2-chlorobenzene and 1-bromo-4-chlorobenzene is expected from the directing effect of the group on the ring (or addition under UV); the other answers apply the wrong directing effect or conditions.

Q10. What is the major product(s) of the reaction of methoxybenzene with Br₂ and FeBr₃?

• A. bromomethane and bromobenzene
• B. 1-bromo-3-methoxybenzene as the only product
• C. 1-bromo-2-methoxybenzene and 1-bromo-4-methoxybenzene(correct answer)
• D. (bromomethoxy)benzene on the side chain

Answer: C.1-bromo-2-methoxybenzene and 1-bromo-4-methoxybenzene is expected from the directing effect of the group on the ring (or addition under UV); the other answers apply the wrong directing effect or conditions.