Q: What is the rate law for an $$S_N1$$ reaction?

$$\text{rate} = k[\text{R-X}]$$

Question 1

Which of the following statements best explains why the rate of an $$S_N1$$ reaction is independent of nucleophile strength?

Accepted Answer

The rate-determining step is the formation of the carbocation intermediate, which does not involve the nucleophile.

Question 2

Given the following alkyl halides, which will undergo $$S_N1$$ solvolysis the fastest in water?

Accepted Answer

2-bromo-2-methylpropane

Question 3

Which of the following best describes the stereochemical outcome of an $$S_N1$$ reaction at a chiral center?

Accepted Answer

A racemic mixture due to planar carbocation intermediate

Question 4

What is the rate law for an $$S_N1$$ reaction?

Accepted Answer

$$	ext{rate} = k[	ext{R-X}]$$

Question 5

According to the Hammond Postulate, the transition state of the rate-determining step in an $$S_N1$$ reaction most closely resembles:

Accepted Answer

The products, because the step is highly endothermic

Question 6

Which of the following solvents would most likely increase the rate of an $$S_N1$$ reaction?

Accepted Answer

Water

Question 7

Why are tertiary alkyl halides more reactive in $$S_N1$$ reactions than primary alkyl halides?

Accepted Answer

Tertiary carbocations are more stable due to hyperconjugation and inductive effects.

Question 8

Which of the following best illustrates hyperconjugation as a stabilizing factor for carbocations?

Accepted Answer

Delocalization of electrons from adjacent $$\sigma$$ bonds into the empty $$p$$ orbital of the carbocation

Question 9

A student is comparing the rates of $$S_N1$$ reactions for the following leaving groups: $$Cl^-$$, $$Br^-$$, $$I^-. $$Which order correctly ranks their leaving group ability and thus the $$S_N1$$ rate?

Accepted Answer

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

Question 10

Which of the following statements about the effect of polar protic solvents on $$S_N1$$ and $$S_N2$$ reactions is correct?

Accepted Answer

Polar protic solvents speed up $$S_N1$$ reactions but slow down $$S_N2$$ reactions.

Question 11

In a solvolysis reaction of an allylic halide with ethanol, two different products are observed. What is the best explanation for this observation?

Accepted Answer

The carbocation intermediate is stabilized by resonance, allowing nucleophilic attack at two positions.

Question 12

Which of the following best describes the energy diagram of an $$S_N1$$ reaction?

Accepted Answer

Two transition states with a carbocation intermediate between them

Question 13

A chemist wants to favor an $$S_N1$$ mechanism over an $$S_N2$$ mechanism. Which combination of substrate and solvent would be most effective?

Accepted Answer

Tertiary alkyl halide in water

Question 14

Which of the following is the best explanation for why $$S_N1$$ reactions often produce racemic mixtures when starting from a chiral alkyl halide?

Accepted Answer

The carbocation intermediate is planar, allowing attack from either side with equal probability.

Question 15

Which of the following best describes the role of the leaving group in the rate-determining step of an $$S_N1$$ reaction?

Accepted Answer

The leaving group departs to form a carbocation in the rate-determining step.

Question 16

Which of the following carbocations is most stabilized by resonance?

Accepted Answer

Benzyl carbocation ($$C_6H_5CH_2^+)$$

Question 17

A student proposes that increasing the concentration of nucleophile will increase the rate of an $$S_N1$$ reaction. Is this correct? Why or why not?

Accepted Answer

No, because the nucleophile only reacts after the rate-determining step.

Question 18

Which of the following best explains why $$S_N1$$ reactions are generally not observed with methyl or primary alkyl halides?

Accepted Answer

Methyl and primary carbocations are too unstable to form under normal conditions.

Question 19

Which of the following is a real-world example where $$S_N1$$ reactivity is important?

Accepted Answer

The hydrolysis of tert-butyl chloride in water to form tert-butyl alcohol

SN1 Reaction Mechanism and Factors Affecting Rate

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