Question 1

Which of the following dienes would react the fastest in a Diels-Alder reaction with a typical dienophile?

Accepted Answer

A diene with electron-donating groups such as $$-$$OCH_3$$ attached to the conjugated system.

Question 2

Which of the following statements best explains why the 2-position is favored over the 3-position in the bromination of thiophene?

Accepted Answer

The arenium ion intermediate formed at the 2-position is stabilized by more resonance structures than at the 3-position.

Question 3

Which compound would react the fastest in an $$S_N1$$ reaction?

Accepted Answer

A tertiary alkyl halide with a good leaving group.

Question 4

Which of the following is the most stable arenium ion (sigma complex) formed during electrophilic aromatic substitution?

Accepted Answer

A sigma complex stabilized by resonance with an electron-donating group such as $$-$$OCH_3$$.

Question 5

Which of the following reagents would you use to convert a benzylic methyl group to a carboxylic acid?

Accepted Answer

$$KMnO_4 ($$potassium permanganate) under basic conditions

Question 6

Which xylene isomer reacts fastest in electrophilic aromatic substitution and why?

Accepted Answer

Ortho-xylene, because the two methyl groups are both activating and their positions allow for more resonance stabilization of the arenium ion.

Question 7

Which of the following compounds will dehydrate most readily under acidic conditions?

Accepted Answer

A tertiary alcohol

Question 8

In the nitration of ortho-xylene, which position will the nitro group most likely add to?

Accepted Answer

The position ortho to one methyl group and meta to the other

Question 9

Which of the following sequences would best synthesize $$p-$$bromobenzoic acid from benzene?

Accepted Answer

1) Friedel-Crafts alkylation (with $$CH_3Cl$$, $$AlCl_3$$), 2) Bromination ($$Br_2$$, $$FeBr_3$$), 3) Oxidation ($$KMnO_4)$$

Question 10

Which of the following best describes the effect of an electron-withdrawing group (such as $$-NO_2$) on the rate of electrophilic aromatic substitution?

Accepted Answer

It decreases the rate by destabilizing the arenium ion intermediate.

Question 11

Which of the following is the correct order of reactivity for the following leaving groups in an $$S_N1$$ reaction: $$Br^-$$, $$Cl^-$$, $$I^-$$, $$F^-$$?

Accepted Answer

$$I^- \u003e Br^- \u003e Cl^- \u003e F^-$$

Question 12

Which of the following best explains why a diene locked in the s-cis conformation reacts faster in the Diels-Alder reaction than one in the s-trans conformation?

Accepted Answer

The s-cis conformation allows for proper orbital overlap between the diene and the dienophile.

Question 13

Which of the following is the correct sequence of reagents to convert benzene to $$p-$$nitrobenzoic acid?

Accepted Answer

1) Friedel-Crafts alkylation ($$CH_3Cl$$, $$AlCl_3$$), 2) Nitration ($$HNO_3$$, $$H_2SO_4$$), 3) Oxidation ($$KMnO_4)$$

Question 14

Which of the following best describes the product of the reaction of methyl benzoate with excess $$HBr$$?

Accepted Answer

Bromomethyl benzoate

Question 15

Which of the following is the best explanation for why a tertiary alcohol dehydrates more readily than a secondary or primary alcohol under acidic conditions?

Accepted Answer

The tertiary carbocation intermediate is more stable due to hyperconjugation and inductive effects.

Question 16

Which of the following is the correct order of stability for arenium ions formed during electrophilic aromatic substitution on benzene derivatives?

Accepted Answer

Arenium ion stabilized by $$-$$OCH_3$$ \u003e unsubstituted benzene \u003e arenium ion stabilized by $$-$$NO_2$$

Question 17

Which of the following best describes the regioselectivity of bromination of 3-alkylthiophene?

Accepted Answer

Bromination is favored at the 2-position because it is alpha to sulfur and less hindered.

Question 18

Which of the following is the correct product of the reaction of benzene with $$Br_2$$ and $$FeBr_3$$?

Accepted Answer

Bromobenzene

Question 19

Which of the following best explains why electron-donating groups increase the rate of electrophilic aromatic substitution?

Accepted Answer

They stabilize the arenium ion intermediate by donating electron density through resonance or induction.

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