Question 1

Which of the following statements best describes the difference between $$S_N2$$ and $$S_N1$$ mechanisms for alkyl halide substitution?

Accepted Answer

$$S_N2$$ reactions are bimolecular and concerted, while $$S_N1$$ reactions are unimolecular and involve a carbocation intermediate.

Question 2

In the $$S_N2$$ reaction of $$(R)-2-$$bromooctane with $$EtS^- in$$ $$EtOH$$, what is the stereochemical outcome at the reaction center?

Accepted Answer

Inversion of configuration

Question 3

Which of the following alkyl halides reacts fastest in an $$S_N2$$ reaction?

Accepted Answer

Methyl bromide

Question 4

What is the effect of a polar aprotic solvent, such as DMF, on the rate of $$S_N2$$ reactions?

Accepted Answer

It increases the nucleophilicity and speeds up the reaction.

Question 5

Which leaving group would result in the fastest $$S_N2$$ reaction rate?

Accepted Answer

$$I^-$$

Question 6

Consider the following reaction: $$CH_3CH_2O^- + CH_3I \rightarrow CH_3CH_2OCH_3 + I^-. If $$the reaction is performed in methanol, which factor most strongly affects the rate?

Accepted Answer

The concentrations of both $$CH_3CH_2O^-$$ and $$CH_3I$$

Question 7

Which statement best explains why $$S_N2$$ reactions do not occur with tertiary alkyl halides?

Accepted Answer

Steric hindrance prevents the nucleophile from attacking the carbon center.

Question 8

In an $$E2$$ elimination reaction, which geometric relationship between the hydrogen and leaving group is required for the reaction to proceed most efficiently?

Accepted Answer

Anti-periplanar

Question 9

Which of the following bases would favor formation of the less substituted alkene in an $$E2$$ elimination?

Accepted Answer

Tert-butoxide ($$(CH_3$)_3CO^-)$$

Question 10

According to Zaitsev's rule, which product will predominate in the $$E2$$ elimination of 2-bromopentane with $$K^+OEt^- in $$ethanol?

Accepted Answer

trans-2-pentene

Question 11

Which of the following statements about $$S_N1$$ and $$E1$$ reactions is correct?

Accepted Answer

Both $$S_N1$$ and $$E1$$ reactions involve a carbocation intermediate.

Question 12

A secondary alkyl halide reacts with $$NaOEt in $$ethanol. What is the expected major product?

Accepted Answer

An alkene via $$E2$$ elimination

Question 13

Which factor increases the amount of $$E1$$ product in a reaction of a tertiary alkyl halide?

Accepted Answer

High reaction temperature

Question 14

What is the effect of a 1,2-hydride shift in an $$S_N1$$ reaction?

Accepted Answer

It increases the stability of the carbocation intermediate.

Question 15

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

Accepted Answer

Racemization

Question 16

In the $$E2$$ elimination of cyclohexyl halides, which conformation is required for the reaction to occur?

Accepted Answer

Both the hydrogen and leaving group must be axial and trans to each other.

Question 17

Which of the following nucleophiles would react fastest in an $$S_N2$$ reaction with methyl iodide in methanol?

Accepted Answer

$$CH_3O^-$$

Question 18

Which of the following statements about the competition between $$S_N2$$ and $$E2$$ reactions is correct?

Accepted Answer

$$E2 is $$favored by strong, bulky bases and hindered alkyl halides.

Question 19

Which of the following best explains why the equilibrium in nucleophilic substitution reactions favors release of the weaker base?

Accepted Answer

The weaker base is a better leaving group.

Chapter 9: The Chemistry of Alkyl Halides – Substitution and Elimination Reactions

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