Organic Substitution Reactions

What are considered good leaving groups in substitution reactions?

• Strong acids

• Weak bases with strong conjugate acids

• Neutral molecules

• Strong bases with weak conjugate acids

Answer explanation

Good leaving groups in substitution reactions are weak bases with strong conjugate acids, as they stabilize the leaving group and facilitate the reaction.

Which of the following is a poor leaving group that can be converted into a good one by protonation?

• Bromide

• Chloride

• Tosylate

• Hydroxide

Answer explanation

Hydroxide is a poor leaving group that can be converted into a good one by protonation, making it the correct choice in this scenario.

What type of carbon is most likely to undergo an SN1 reaction?

• Secondary carbon

• Quaternary carbon

• Primary carbon

• Tertiary carbon

Answer explanation

Tertiary carbon is most likely to undergo an SN1 reaction due to the stability of the carbocation intermediate formed in the process.

Which solvent type favors SN1 mechanisms?

• Ionic

• Non-polar

• Polar aprotic

• Polar protic

Answer explanation

Polar protic solvents favor SN1 mechanisms due to their ability to stabilize carbocation intermediates by hydrogen bonding.

What is the role of the nucleophile in an SN2 reaction?

• It acts as a solvent

• It waits for the leaving group to leave

• It stabilizes the transition state

• It is an active participant in the rate-determining step

Answer explanation

The nucleophile is an active participant in the rate-determining step of an SN2 reaction.

Which of the following is a characteristic of strong nucleophiles?

• They are weakly polarizable

• They prefer SN1 mechanisms

• They are uncharged

• They are often charged

Answer explanation

Strong nucleophiles are often charged, making them more reactive in nucleophilic substitution reactions.

What effect does a polar aprotic solvent have on an SN2 reaction?

• It stabilizes the carbocation

• It favors the reaction by not bonding to the nucleophile

• It disfavors the reaction by bonding to the nucleophile

• It has no effect on the reaction

Answer explanation

A polar aprotic solvent favors the SN2 reaction by not bonding to the nucleophile, allowing it to attack the substrate more easily.

Which of the following substrates is unlikely to undergo an SN2 reaction?

• Chlorobenzene

• Methyl chloride

• Ethyl bromide

• Isopropyl chloride

Answer explanation

Chlorobenzene is unlikely to undergo an SN2 reaction due to the lack of a good leaving group on the benzene ring.

What is the effect of substrate structure on SN2 reactions?

• Primary carbons are most reactive

• All carbons react equally

• Secondary carbons are most reactive

• Tertiary carbons are most reactive

Answer explanation

Substrate structure affects SN2 reactions, with primary carbons being the most reactive due to less steric hindrance compared to secondary or tertiary carbons.

Which of the following is not a good leaving group?

• Triflate

• Mesylate

• Tosylate

• Hydroxide

Answer explanation

Hydroxide is not a good leaving group due to its poor ability to stabilize negative charge, unlike triflate, mesylate, and tosylate which are good leaving groups.