Free Benzene and Aromatic Compounds MCQs with Answers
172 Benzene and Aromatic Compounds MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Benzene has a planar ring of delocalised π electrons, giving aromatic stability and equal carbon-carbon bond lengths. The topic covers resonance, electrophilic substitution reactions such as nitration, halogenation, sulphonation and Friedel-Crafts reactions, along with substituent effects and the distinction between substitution in benzene and addition in ordinary alkenes.
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172 questions · page 1 of 9
- A. the molecular formula C6H6
- B. the ring shape of the molecule
- C. why benzene resists addition reactions and has all its carbon to carbon bonds of equal length
- D. why benzene contains only carbon and hydrogen
Explanation: Alternating single and double bonds would predict two different bond lengths and the ready addition reactions of an alkene, but experiment…
Correct answer: why benzene resists addition reactions and has all its carbon to carbon bonds of equal length- A. preserves the stable delocalised pi system
- B. produces a smaller molecule
- C. requires no catalyst
- D. is always exothermic
Explanation: Addition would destroy the aromatic sextet and lose the large resonance stabilisation, whereas replacing a hydrogen leaves the delocalised…
Correct answer: preserves the stable delocalised pi system- A. dilute nitric acid alone at room temperature
- B. a mixture of concentrated nitric and concentrated sulphuric acids at about 50 to 60 degrees Celsius
- C. sodium nitrate solution
- D. nitrogen dioxide gas in sunlight
Explanation: Sulphuric acid protonates nitric acid so that it loses water and generates the nitronium ion, which is the actual electrophile attacking…
Correct answer: a mixture of concentrated nitric and concentrated sulphuric acids at about 50 to 60 degrees Celsius- A. has a pleasant smell
- B. contains only carbon and hydrogen
- C. reacts readily by addition
- D. is planar, cyclic and has a delocalised system of six pi electrons obeying Huckel's rule
Explanation: Aromaticity in the modern sense requires a planar cyclic conjugated system containing 4n plus 2 pi electrons, which for benzene means six…
Correct answer: is planar, cyclic and has a delocalised system of six pi electrons obeying Huckel's rule- A. Aromaticity
- B. Stability
- C. To follow Huckel rule
- D. High reactivity
Explanation: The delocalised ring of six pi electrons makes benzene unusually stable, so it resists addition and reacts only under forcing conditions…
Correct answer: High reactivity- A. Electrophilic addition
- B. Electrophilic substitution
- C. Free radical substitution
- D. Free radical halogenation
Explanation: Iron three chloride acts as a halogen carrier, polarising the chlorine molecule to generate an electrophile that attacks the electron rich…
Correct answer: Electrophilic substitution- A. Addition reaction
- B. Substitution reactions
- C. Halogenation
- D. All of these
Explanation: Benzene mainly undergoes electrophilic substitution because substitution preserves its especially stable aromatic ring, whereas addition…
Correct answer: Substitution reactions- A. Unsaturations
- B. Cyclic structure
- C. Presence of 4nπ electrons
- D. Presence of 4n+2π electrons
Explanation: Aromatic compounds require a cyclic, planar, continuously conjugated system containing 4n + 2 pi electrons, according to Huckel's rule.
Correct answer: Presence of 4n+2π electrons- A. +I and +R effect
- B. -1 and +R effect
- C. +1 and -R effect
- D. -I and -R effect
Explanation: Chlorine withdraws electron density through sigma bonds because of its electronegativity, giving a -I effect.
Correct answer: -1 and +R effect- A. nitration
- B. halogenation
- C. sulphonation
- D. amination
Explanation: Nitration is the introduction of a nitro group, -NO2, into an organic molecule, commonly by treating an aromatic compound with…
Correct answer: nitration- A. Glycol
- B. Glyoxal
- C. Vicinal diol
- D. Both B & C
Explanation: Ozonolysis breaks the carbon-carbon bonds of benzene and produces three molecules of glyoxal, OHC-CHO.
Correct answer: Glyoxal- A. Oxidation
- B. Polymerization
- C. Dehydration
- D. Condensation
Explanation: Three acetylene molecules combine in a cyclic process to form one benzene molecule, so the reaction is a cyclotrimerisation, a type of…
Correct answer: Polymerization- A. Substitution reaction
- B. Addition reaction
- C. Elimination reaction
- D. Oxidation reaction
Explanation: Heating benzene with air over V2O5 oxidises the ring, commonly producing maleic anhydride, so the reaction is an oxidation reaction.
Correct answer: Oxidation reaction- A. NO3
- B. NO
- C. NO2-
- D. NO2+
Explanation: The nitronium ion is NO2+, formed in the nitrating mixture from nitric acid and sulfuric acid, and it acts as the electrophile in benzene…
Correct answer: NO2+- A. Substitution reaction
- B. Addition reaction
- C. Polymerization reactions
- D. Oxidation reactions
Explanation: Benzene commonly undergoes electrophilic substitution and can undergo addition or oxidation under appropriate severe or catalytic…
Correct answer: Polymerization reactions- A. diphenyl amine
- B. diphenyl methane
- C. naphthalene
- D. biphenyl
Explanation: Naphthalene is a fused cyclic aromatic compound because two benzene rings share a pair of adjacent carbon atoms and form one fused ring…
Correct answer: naphthalene- A. acetylene
- B. N-hexane
- C. Benzene sulphonic acid
- D. Sodium benzoate
Explanation: N-hexane undergoes catalytic dehydrocyclisation, losing hydrogen and forming a six-membered aromatic ring, benzene.
Correct answer: N-hexane- A. Specific gravity method
- B. Vapour density method
- C. X-ray diffraction method
- D. Distillation methos
Explanation: Vapour density is related to molecular mass by molecular mass = 2 x vapour density when the vapour is measured relative to hydrogen.
Correct answer: Vapour density method- A. o - chloronitrobenzene
- B. p - chloronitrobenzene
- C. m - chloronitrobenzene
- D. A & B
Explanation: Chlorine is deactivating but ortho-para directing because its lone pairs can donate by resonance into the benzene ring.
Correct answer: A & B- A. Glyoxime
- B. Benzaldehyde
- C. Glycol
- D. Glyoxal
Explanation: Benzene adds three ozone molecules, one across each of its three double-bond equivalents, and hydrolysis of the ozonide produces 3 moles…
Correct answer: GlyoxalBenzene and Aromatic Compounds MCQs: common questions
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