Question 1

Which of the following statements best explains why electrophilic aromatic substitution (EAS) is favored over electrophilic addition in arenes?

Accepted Answer

Arene pi bonds have special resonance stability, making substitution energetically favorable.

Question 2

What is the first step in the general mechanism of electrophilic aromatic substitution (EAS)?

Accepted Answer

Prepare the electrophile.

Question 3

During the nitration of benzene, which species acts as the electrophile?

Accepted Answer

NO$$_2^+$$

Question 4

Which reagent combination is required to generate the nitronium ion ($$NO_2$$^+$$) for benzene nitration?

Accepted Answer

$$HNO_3 + H_2SO_4$

Question 5

In the sulfonation of benzene, what is the unique mechanistic step compared to other EAS reactions?

Accepted Answer

Protonation of the sulfonic acid group after substitution.

Question 6

What is the role of FeBr$$_3 in $$the halogenation of benzene?

Accepted Answer

It generates the electrophilic bromine species.

Question 7

Which halogen is the most reactive in electrophilic aromatic substitution, and why?

Accepted Answer

Fluorine, because it forms the most reactive electrophile.

Question 8

Why are Friedel-Crafts alkylations rarely used in synthesis?

Accepted Answer

Carbocations formed during the reaction can rearrange, leading to poor yields and polyalkylation.

Question 9

Which of the following is a major advantage of Friedel-Crafts acylation over alkylation?

Accepted Answer

It avoids carbocation rearrangements and polyalkylation.

Question 10

What is the key reactive intermediate formed in Friedel-Crafts acylation?

Accepted Answer

Acylium ion ($$RCO^+)$$

Question 11

Which reagent is used in the Clemmensen reduction to convert aryl ketones to hydrocarbons?

Accepted Answer

$$Zn(Hg)$$, $$HCl$$

Question 12

Which substituent is a very strongly activating group and directs substitution to the ortho and para positions?

Accepted Answer

$$-NH_2$

Question 13

Why does the para product often have the lowest activation energy ($$E_{act}) in $$EAS, but is not always the major product?

Accepted Answer

Steric hindrance at the para position can reduce its formation.

Question 14

Which of the following substituents is meta-directing and strongly deactivating in EAS?

Accepted Answer

$$-COOH$$

Question 15

What is the major product when $$p-$$xylene (1,4-dimethylbenzene) reacts with acetic anhydride and $$AlCl_3$$?

Accepted Answer

Acetylation at the ortho position to one methyl group

Question 16

Which of the following best describes the effect of halogen substituents on benzene in EAS?

Accepted Answer

They are deactivating but still ortho/para-directing.

Question 17

A benzene ring with a nitro group and a methyl group undergoes bromination. Where will the bromine most likely add?

Accepted Answer

Meta to the nitro group

Question 18

Which of the following is true about the Wolff-Kishner reduction?

Accepted Answer

It reduces aldehydes and ketones to hydrocarbons under basic conditions.

Question 19

Which of the following best explains why $$-NH_2$ is more activating than -OH$ as a substituent on benzene?

Accepted Answer

$$-NH_2$ donates electrons more effectively via resonance and induction.

Electrophilic Aromatic Substitution and Friedel-Crafts Reactions

Study Guide - Practice Questions