Question 1

Which of the following substituents on benzene will increase the rate of electrophilic aromatic substitution and direct incoming electrophiles to the ortho and para positions?

Accepted Answer

OCH$_3$

Question 2

Consider the nitration of toluene (methylbenzene). Which positions on the ring are favored for substitution, and why?

Accepted Answer

Ortho and para, because the methyl group is an electron donating group and stabilizes the sigma complex at these positions

Question 3

Which of the following groups is classified as an electron withdrawing group (EWG) and is a meta-director in electrophilic aromatic substitution?

Accepted Answer

NO$_2$

Question 4

Why does anisole (methoxybenzene) act as an activator in electrophilic aromatic substitution reactions?

Accepted Answer

Because the methoxy group donates electrons to the ring via resonance, increasing electron density and nucleophilicity

Question 5

In the reaction of bromobenzene with an electrophile, bromine is a deactivator but directs substitution to the ortho and para positions. What explains this behavior?

Accepted Answer

Bromine withdraws electrons by induction but stabilizes the sigma complex at ortho and para positions via resonance

Question 6

Which of the following best describes the effect of a nitro group on the reactivity and directive effects in electrophilic aromatic substitution?

Accepted Answer

Deactivates the ring and directs to meta position

Question 7

When an isopropyl group (iPr) is attached to benzene, why is the para product favored over the ortho product in nitration?

Accepted Answer

Because the isopropyl group is larger than methyl, causing steric hindrance at the ortho position

Question 8

Which of the following statements about resonance stabilization of the sigma complex in electrophilic aromatic substitution is correct?

Accepted Answer

The ortho sigma complex with an electron donating group has more resonance forms and is lower in energy than the meta sigma complex

Question 9

A benzene ring substituted with a carboxylic acid group (COOH) undergoes electrophilic aromatic substitution. Which position is favored for substitution and why?

Accepted Answer

Meta, because COOH is an electron withdrawing group and destabilizes the sigma complex at ortho and para positions

Question 10

Which of the following is NOT an electron donating group (EDG)?

Accepted Answer

NO$_2$

Question 11

In the energy diagram for electrophilic aromatic substitution, which product is favored when an activator is present on the benzene ring?

Accepted Answer

Ortho and para products, because their sigma complexes are lower in energy than the meta

Question 12

Which of the following best explains why electron withdrawing groups (EWGs) are meta-directors in electrophilic aromatic substitution?

Accepted Answer

EWGs stabilize the sigma complex at the meta position by avoiding placing the positive charge adjacent to the EWG

Question 13

If a benzene ring has both a methoxy group (OCH$_3$) and a nitro group (NO$_2$), which group will dominate the directive effects in an electrophilic aromatic substitution reaction?

Accepted Answer

The methoxy group, because it is a stronger activator

Question 14

Which of the following is a correct statement about halogen substituents (e.g., Br) on benzene in electrophilic aromatic substitution?

Accepted Answer

Halogens are deactivators but ortho, para-directors due to resonance stabilization

Question 15

Which of the following functional groups would make benzene less reactive toward electrophilic aromatic substitution?

Accepted Answer

SO$_3$H

Question 16

A student is asked to predict the major product of the nitration of methylbenzene (toluene). Which product is most likely, and what is the reasoning?

Accepted Answer

Para-nitrotoluene, because methyl is an electron donating group and steric hindrance reduces ortho substitution

Question 17

Which of the following best describes the effect of resonance on the stability of the sigma complex in electrophilic aromatic substitution?

Accepted Answer

More resonance forms generally increase the stability of the sigma complex

Question 18

Which of the following is a plausible reason why the meta product is favored in the nitration of nitrobenzene?

Accepted Answer

The meta sigma complex avoids placing the positive charge adjacent to the electron withdrawing nitro group, resulting in lower energy

Question 19

Which of the following groups would NOT be expected to activate the benzene ring toward electrophilic aromatic substitution?

Accepted Answer

CO$_2$R

Question 20

Which of the following statements about directive effects in electrophilic aromatic substitution is correct?

Accepted Answer

Electron donating groups are ortho, para-directors

Electrophilic Aromatic Substitution: Substituent Effects Study Guide

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