NEET Chemistry: Friedel-Crafts reactions Practice Questions
15 free multiple-choice questions on Friedel-Crafts reactions (Aromatic Hydrocarbons) for NEET Chemistry, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.
Practice thousands more NEET questions in the app →Q1. The reaction of benzene with a Friedel-Crafts acid catalyst results in the substitution of hydrogen atoms on the ring by an alkyl group. This type of reaction is classified as:
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Correct answer: B — Electrophilic aromatic substitution
Friedel-Crafts reactions are classic examples of Electrophilic Aromatic Substitution (EAS), where an electrophile attacks the benzene ring.
Q2. Which of the following reagents is used to catalyze the Friedel-Crafts alkylation reaction?
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Correct answer: A — AlCl₃
Aluminum chloride (AlCl₃) acts as a Lewis acid catalyst, complexing with the alkyl halide to generate the electrophile (R⁺) necessary for the reaction.
Q3. In the Friedel-Crafts reaction, the reaction occurs at which part of the aromatic ring?
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Correct answer: B — The π electron system of the ring
Electrophilic substitution reactions, like Friedel-Crafts, occur via the attack of the electrophile on the π electron system of the aromatic ring, breaking the aromaticity temporarily.
Q4. In Friedel-Crafts acylation, which group is typically used to introduce an acyl group (RCO-) onto the benzene ring?
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Correct answer: A — Acyl chlorides or acid anhydrides
Friedel-Crafts acylation involves reacting an aromatic compound with an acylating agent (like acyl chloride or anhydride) and a Lewis acid catalyst, leading to the introduction of the acyl group.
Q5. The product formed by Friedel-Crafts alkylation involves the addition of which group to the benzene ring?
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Correct answer: D — Alkyl group (R)
Friedel-Crafts alkylation specifically introduces an alkyl group (R) onto the benzene ring via electrophilic substitution.
Q6. The reaction of benzene with CH₃Cl in the presence of AlCl₃ results in the formation of which product?
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Correct answer: D — Toluene
This is the Friedel-Crafts Alkylation. The electrophile (CH₃⁺) attacks the benzene ring, resulting in the addition of a methyl group, yielding Toluene.
Q7. In the Friedel-Crafts alkylation reaction, which of the following compounds is generally least reactive toward the electrophile (R⁺)?
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Correct answer: B — Chlorobenzene
Chlorobenzene is less reactive than benzene towards electrophilic substitution because the halogen atom deactivates the ring slightly towards further electrophilic attack, although it is still substituted. Compared to the others, it exhibits reduced reactivity.
Q8. Friedel-Crafts reactions are examples of which type of reaction on aromatic hydrocarbons?
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Correct answer: B — Electrophilic aromatic substitution
Friedel-Crafts reactions involve the substitution of hydrogen atoms on the benzene ring by an electrophile, which is the definition of Electrophilic Aromatic Substitution (EAS).
Q9. The reaction mechanism for electrophilic substitution on benzene involves the attack of the electrophile on the π-electron system, leading to the formation of a transient intermediate known as the:
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Correct answer: B — Sigma complex
The attack of the electrophile results in the formation of a resonance-stabilized carbocation intermediate known as the sigma complex.
Q10. Which of the following compounds is typically used as the acylating agent in the Friedel-Crafts acylation reaction?
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Correct answer: A — Acyl halides
The Friedel-Crafts acylation requires an acylating agent, which is usually an acyl halide (like RCOCl) or an acid anhydride, to react with the Lewis acid to form the acylium ion electrophile.
Q11. The primary function of a Lewis acid catalyst, such as AlCl₃, in Friedel-Crafts reactions is to:
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Correct answer: A — Coordinate with the electrophile and generate a highly reactive carbocation
The Lewis acid catalyst coordinates with the electrophile (the acylium ion or alkyl carbocation) to generate a highly reactive electrophile that attacks the aromatic ring.
Q12. Which of the following compounds acts as the electrophile in the Friedel-Crafts alkylation reaction?
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Correct answer: A — Alkyl cations
In Friedel-Crafts alkylation, the electrophile is typically generated from an alkyl halide and a Lewis acid catalyst, forming a carbocation which attacks the aromatic ring.
Q13. Which of the following is the primary product obtained when benzene is reacted with acetyl chloride in the presence of AlCl₃ (Friedel-Crafts acylation)?
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Correct answer: A — Acetophenone
The reaction of benzene with an acylating agent (like acetyl chloride) yields the ketone product, acetophenone, as the primary outcome in acylation.
Q14. Which type of Friedel-Crafts reaction is typically used when the goal is to introduce a carbonyl group (C=O) onto the aromatic ring?
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Correct answer: D — Friedel-Crafts Acylation
Friedel-Crafts Acylation involves reacting the aromatic ring with acyl halides and a Lewis acid to introduce an acyl group, forming a ketone or aldehyde upon subsequent workup.
Q15. Which substance is essential to generate the electrophile in the Friedel-Crafts alkylation reaction when using an alkyl halide and a Lewis acid?
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Correct answer: C — Lewis Acid
The Lewis acid (e.g., AlCl3) coordinates with the alkyl halide to generate the highly reactive carbocation, which acts as the electrophile.
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