Question 1

Which of the following statements best explains why tertiary alkyl halides rarely undergo $$S_N2$$ reactions?

Accepted Answer

Tertiary alkyl halides are too sterically hindered for the nucleophile to perform a backside attack required in $$S_N2.$$

Question 2

A student attempts to convert 2-bromopropane to 2-methoxypropane using sodium methoxide in methanol. Which mechanism is most likely to occur?

Accepted Answer

$$S_N1$$, because the secondary substrate and polar protic solvent favor carbocation formation.

Question 3

Which of the following is the best leaving group for a substitution reaction?

Accepted Answer

$$CH_3COO^-$$

Question 4

Why does the use of a bulky base such as potassium tert-butoxide ($$KO^tBu) $$favor the formation of the Hofmann (less substituted) alkene in an E2 elimination?

Accepted Answer

Bulky bases preferentially remove the most accessible hydrogen, which is usually on the least substituted carbon.

Question 5

Which solvent would most effectively increase the rate of an $$S_N2$$ reaction involving a charged nucleophile?

Accepted Answer

Dimethyl sulfoxide (DMSO)

Question 6

A primary alkyl bromide reacts with sodium cyanide ($$NaCN) in $$acetonitrile. What is the major product and mechanism?

Accepted Answer

A nitrile via $$S_N2$$ substitution

Question 7

Which of the following factors does NOT increase nucleophilicity for atoms in the same row of the periodic table?

Accepted Answer

Larger atomic radius

Question 8

In an E2 elimination, which geometric relationship between the leaving group and the hydrogen being abstracted is required?

Accepted Answer

Antiperiplanar

Question 9

Which of the following statements about $$S_N1$$ reactions is TRUE?

Accepted Answer

The reaction proceeds through a carbocation intermediate.

Question 10

A student wants to convert an alcohol to a good leaving group for substitution. Which reagent would be most effective?

Accepted Answer

Tosyl chloride ($$TsCl)$$

Question 11

Which of the following best describes the effect of a polar protic solvent on an $$S_N2$$ reaction?

Accepted Answer

It stabilizes the nucleophile, decreasing its reactivity and slowing the reaction.

Question 12

Which of the following is a common exception to Zaitsev's rule in E2 eliminations?

Accepted Answer

Use of a bulky base, favoring the Hofmann product

Question 13

Which of the following nucleophiles would be most effective in an $$S_N2$$ reaction with methyl bromide in DMSO?

Accepted Answer

$$OH^-$$

Question 14

What is the major product when 2-bromobutane is treated with sodium ethoxide ($$NaOEt) in $$ethanol at elevated temperature?

Accepted Answer

2-butene via E2 elimination (Zaitsev product)

Question 15

Which of the following statements about the stereochemistry of $$S_N2$$ reactions is correct?

Accepted Answer

The product is inverted relative to the starting material due to backside attack.

Question 16

Which of the following best explains why $$OH^- is a $$poor leaving group in substitution and elimination reactions?

Accepted Answer

$$OH^- is a $$strong base and forms an unstable anion when it leaves.

Question 17

Which of the following would most likely favor an E1 elimination over an E2 elimination?

Accepted Answer

A tertiary substrate and a weak base in polar protic solvent

Question 18

Which of the following is true regarding the rate-determining step of an $$S_N2$$ reaction?

Accepted Answer

It involves both the nucleophile and the substrate.

Question 19

A student treats 1-bromopentane with sodium thiolate ($$NaS^-) in $$DMF. What is the expected major product?

Accepted Answer

1-thiopentane via $$S_N2$$ substitution

Question 20

Which of the following best describes the role of resonance in determining nucleophilicity?

Accepted Answer

Resonance decreases nucleophilicity by stabilizing the negative charge.

Ochem CH 10 Substitution and Elimination Reactions

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