Question 1

Which of the following statements best explains why iodide ($$I^-) is a $$better leaving group than fluoride ($$F^-) in $$nucleophilic substitution reactions?

Accepted Answer

Iodide is a weaker base and its conjugate acid ($$HI) $$has a lower $$pK_a$$ than fluoride's conjugate acid ($$HF$$), making $$I^-$$ more stable as a leaving group.

Question 2

A primary alkyl halide reacts with a strong nucleophile in a polar aprotic solvent. Which mechanism is most likely to occur?

Accepted Answer

S$$_N2 $$substitution

Question 3

Which of the following best describes the rate law for an S$$_N1 $$reaction?

Accepted Answer

rate $$= k[	ext{RX}]$$

Question 4

In an E2 elimination of an acyclic alkyl halide, which geometric arrangement of the hydrogen and leaving group is required for the reaction to proceed?

Accepted Answer

Anti-periplanar

Question 5

Which of the following nucleophiles would be expected to favor an S$$_N2 $$mechanism over S$$_N1 $$when reacting with a secondary alkyl halide?

Accepted Answer

$$OH^-$$

Question 6

A tertiary alkyl halide is treated with a weak base in ethanol. Which product(s) would you expect?

Accepted Answer

A mixture of alkene (E1) and substitution (S$$_N1) $$products

Question 7

Which of the following statements about carbocation rearrangements is correct?

Accepted Answer

A 1,2-hydride or 1,2-alkyl shift can convert a secondary carbocation to a tertiary carbocation.

Question 8

Which factor does NOT increase nucleophilicity in substitution reactions at sp$$^3$$ carbon?

Accepted Answer

Increasing steric hindrance

Question 9

Which of the following best explains why S$$_N2 $$reactions result in inversion of configuration at the stereocenter?

Accepted Answer

The nucleophile attacks from the opposite side of the leaving group (backside attack).

Question 10

Which of the following is true regarding the reactivity of alcohols in substitution and elimination reactions?

Accepted Answer

Alcohols require activation (e.g., by strong acid or conversion to tosylate) to become good leaving groups.

Question 11

Which of the following best describes the selectivity of E2 elimination reactions?

Accepted Answer

E2 reactions are regioselective (favoring more substituted alkene) and stereospecific (anti-periplanar arrangement).

Question 12

Which of the following statements about epoxide ring-opening reactions is correct?

Accepted Answer

Epoxide ring-opening by nucleophiles occurs via backside attack, leading to stereospecific products.

Question 13

Which of the following is the correct rate law for an E2 elimination reaction?

Accepted Answer

rate $$= k[	ext{RX}][	ext{B}]$$

Question 14

A secondary alkyl halide reacts with a strong, bulky base. Which product is most likely?

Accepted Answer

Elimination product via E2

Question 15

Which of the following is a 'good' leaving group for nucleophilic substitution, based on $$pK_a$$ values?

Accepted Answer

$$Br^-$$

Question 16

Which of the following best describes the stereochemical outcome of an S$$_N1 $$reaction at a chiral center?

Accepted Answer

Racemization of stereochemistry

Question 17

Which of the following statements is true regarding the competition between substitution and elimination reactions?

Accepted Answer

Strong bases favor elimination (E2), while weak bases favor elimination (E1) and substitution (S$$_N1).$$

Question 18

Which of the following is most likely to undergo a carbocation rearrangement during a reaction?

Accepted Answer

A secondary alkyl halide undergoing S$$_N1 $$substitution

Question 19

Which of the following is NOT a factor that determines whether a reaction will proceed via S$$_N1$$, S$$_N2$$, E1, or E2 mechanism?

Accepted Answer

Color of the reactants

Key Concepts in Nucleophilic Substitution and Elimination Reactions (CHEM 3305 Exam 3)

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