Question 1

Which of the following statements best describes the role of a Lewis acid in the Friedel-Crafts alkylation of benzene?

Accepted Answer

It generates a carbocation by accepting a halide ion from the alkyl halide.

Question 2

Which of the following substituents on a benzene ring is most likely to activate the ring toward electrophilic aromatic substitution, and why?

Accepted Answer

A methyl group, because it donates electrons via hyperconjugation.

Question 3

During the nitration of benzene, which intermediate is formed after the initial attack by benzene on the nitronium ion ($$NO_2$$^+$$)?

Accepted Answer

A sigma complex (arenium ion)

Question 4

Which of the following best explains why Friedel-Crafts acylation does not suffer from carbocation rearrangements, unlike alkylation?

Accepted Answer

The acylium ion formed ($$RCO^+) is $$stabilized by resonance and does not rearrange.

Question 5

Which of the following is the correct product of the Diels-Alder reaction between 1,3-butadiene and ethene?

Accepted Answer

Cyclohexene

Question 6

In the syn dihydroxylation of alkenes using osmium tetroxide ($$OsO_4$$), what is the stereochemical outcome of the reaction?

Accepted Answer

Syn diol formation

Question 7

Which of the following best describes the mechanism of nucleophilic aromatic substitution (NAS) in a benzene ring with a nitro group at the ortho or para position?

Accepted Answer

NAS proceeds via an addition-elimination mechanism, forming a Meisenheimer complex.

Question 8

Which of the following is the correct resonance structure for the arenediazonium ion ($$PhN_2$$^+$$)?

Accepted Answer

$$Ph-N\equiv N^+$$

Question 9

A student attempts to synthesize an alkene using the Wittig reaction. Which of the following reagents is required to generate the ylide for this reaction?

Accepted Answer

Triphenylphosphine and an alkyl halide, followed by a strong base

Question 10

Which of the following best describes the product formed when acetylene ($$HC\equiv CH) $$reacts with sodium amide ($$NaNH_2$$)?

Accepted Answer

Acetylide ion ($$HC\equiv C^-)$$

Question 11

Which of the following is a plausible reason why a Friedel-Crafts alkylation might fail when using a nitrobenzene as the substrate?

Accepted Answer

The nitro group deactivates the ring, making it less reactive toward electrophilic substitution.

Question 12

Which of the following best explains why the ortho/para positions are favored in electrophilic aromatic substitution when a methoxy group ($$-$$OCH_3$$) is attached to benzene?

Accepted Answer

The methoxy group donates electrons via resonance, stabilizing the ortho/para carbocation.

Question 13

Which of the following is the correct sequence of steps in the bromination of benzene?

Accepted Answer

Activation of $$Br_2 by$$ $$FeBr_3$$, formation of sigma complex, deprotonation

Question 14

A chemist wants to synthesize 1,2-dihydroxycyclohexane from cyclohexene. Which reagent should they use, and what is the expected stereochemistry?

Accepted Answer

$$OsO_4$$; syn addition

Question 15

Which of the following is a key feature of the Diels-Alder reaction that makes it useful in organic synthesis?

Accepted Answer

It forms six-membered rings with high regio- and stereoselectivity.

Question 16

Which of the following is the correct product when benzene reacts with $$CH_3COCl in $$the presence of $$AlCl_3$$?

Accepted Answer

Acetophenone ($$C_6H_5COCH_3)$$

Question 17

Which of the following best describes the effect of a sulfonic acid group ($$-SO_3H) on $$the reactivity of benzene toward electrophilic aromatic substitution?

Accepted Answer

It deactivates the ring by withdrawing electrons via resonance and induction.

Question 18

Which of the following is the correct order of reactivity toward electrophilic aromatic substitution for the following substituents: $$-NO_2$, $$-$$CH_3$$, $$-$$OCH_3$$?

Accepted Answer

$$-$$OCH_3$$ \u003e -CH_3$ \u003e -NO_2$

Question 19

Which of the following best describes the outcome when an acetylide ion ($$RC\equiv C^-) $$reacts with a primary alkyl halide?

Accepted Answer

It forms a new carbon-carbon bond via nucleophilic substitution.

Question 20

Which of the following is a plausible reason why the Wittig reaction is preferred over other alkene-forming reactions in pharmaceutical synthesis?

Accepted Answer

It allows for precise control of alkene stereochemistry and avoids rearrangements.

Key Mechanisms and Reactions for Organic Chemistry Exam 1 (Chapters 12–14)

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