Q: During the bromination of benzene, which species acts as the electrophile that attacks the aromatic ring?

$$\mathrm{Br}^+\text{-}\mathrm{FeBr}_3$$\text{ (the activated bromine complex)}

Question 1

Which of the following statements best explains why benzene undergoes electrophilic aromatic substitution (EAS) rather than addition reactions under typical conditions?

Accepted Answer

EAS reactions preserve the aromaticity of benzene, which is energetically favorable.

Question 2

During the bromination of benzene, which species acts as the electrophile that attacks the aromatic ring?

Accepted Answer

$$\mathrm{Br}^+	ext{-}\mathrm{FeBr}_3$$	ext{ (the activated bromine complex)}

Question 3

What is the role of $$\mathrm{H_2SO_4} in $$the nitration of benzene?

Accepted Answer

It acts as a catalyst to generate the nitronium ion ($$\mathrm{NO_2$^+}$$), the true electrophile.

Question 4

Which of the following substituents on a benzene ring will direct incoming electrophiles to the ortho and para positions and increase the rate of EAS reactions?

Accepted Answer

$$\mathrm{$$OCH_3$$}$$

Question 5

Why does anisole ($$\mathrm{C_6H_5OCH_3}) $$undergo nitration much faster than benzene?

Accepted Answer

The methoxy group donates electron density to the ring via resonance, stabilizing the sigma complex.

Question 6

Which of the following is a limitation of the Friedel-Crafts alkylation reaction?

Accepted Answer

It can lead to polyalkylation because the product is more reactive than benzene.

Question 7

A student attempts to nitrate nitrobenzene. Which major product will be formed?

Accepted Answer

Meta-dinitrobenzene

Question 8

Which reagent is required to reduce a nitro group ($$\mathrm{NO_2$}) on an $$aromatic ring to an amino group ($$\mathrm{NH_2$}$$)?

Accepted Answer

Zn, Sn, or Fe in dilute acid

Question 9

Which statement best describes the directing effects of halogens in EAS reactions?

Accepted Answer

Halogens are deactivating but still ortho/para-directing due to resonance stabilization.

Question 10

Which of the following best explains why the Birch reduction of benzene produces 1,4-cyclohexadiene rather than a conjugated diene?

Accepted Answer

The mechanism involves selective reduction of two non-adjacent double bonds due to electron localization.

Question 11

Which of the following is true about nucleophilic aromatic substitution (NAS) reactions?

Accepted Answer

Electron-withdrawing groups ortho or para to the leaving group activate the ring for NAS.

Question 12

A chemist wants to synthesize ethylbenzene from benzene. Which reaction should they use?

Accepted Answer

Friedel-Crafts alkylation with ethyl chloride and $$\mathrm{$$AlCl_3$$}$$

Question 13

Which of the following statements about the energy diagram for bromination of benzene is correct?

Accepted Answer

The rate-limiting step is the formation of the sigma complex (arenium ion).

Question 14

Which of the following best describes the effect of multiple substituents on the directing outcome of EAS reactions?

Accepted Answer

If directing effects oppose, the most powerful activating group dominates.

Question 15

Which of the following is a real-world application of the Suzuki reaction?

Accepted Answer

Coupling an aryl halide with an alkylboronic acid using a palladium catalyst to form biaryl compounds.

Question 16

Which of the following statements is true regarding side-chain halogenation of alkylbenzenes?

Accepted Answer

Bromination occurs selectively at the benzylic position.

Question 17

Which of the following best explains why benzylic halides are highly reactive in $$\mathrm{S_N2}$$ reactions?

Accepted Answer

The transition state is stabilized by resonance with the aromatic ring.

Question 18

Which of the following is the best method to add an amino group to a benzene ring?

Accepted Answer

Nitration followed by reduction with Zn, Sn, or Fe in dilute acid

Question 19

Which of the following statements about sulfonation of benzene is correct?

Accepted Answer

Sulfonation is reversible; the sulfonic acid group can be removed by heating in dilute $$\mathrm{H_2SO_4}.$$

Reactions of Aromatic Compounds: Electrophilic and Nucleophilic Substitution, Directing Effects, and Side-Chain Chemistry

Guida di studio - Domande di pratica

Study guide - Flashcard