Question 1

Which of the following statements best explains why two molecules of HBr can add to the triple bond in an alkyne, but only one molecule of water can add?

Accepted Answer

Alkynes can undergo two successive electrophilic additions with HBr, forming a geminal dihalide, but hydration leads to a ketone via tautomerization, preventing further addition.

Question 2

Arrange the following compounds according to the stability of the carbocation intermediate formed when they react with nucleophiles: $$CH_3CH_2CH_2^+$$, $$(CH_3$)_3C^+$$, $$CH_2$$=$$CHCH_2$$^+$$.

Accepted Answer

$$(CH_3$)_3C^+ \u003e CH_2$=$$CHCH_2$$^+ \u003e CH_3CH_2CH_2^+$$

Question 3

Which of the following is the best leaving group in nucleophilic substitution reactions (SN2)?

Accepted Answer

$$Br^-$$

Question 4

In the SN2 reaction, which compound reacts the fastest?

Accepted Answer

Methyl bromide

Question 5

Which of the following compounds will react fastest with ethyl iodide in an SN2 reaction?

Accepted Answer

Methanethiol

Question 6

Which of the following is the most stable carbocation?

Accepted Answer

$$(CH_3$)_3C^+$$

Question 7

Which of the following statements best describes the difference between SN1 and SN2 mechanisms?

Accepted Answer

SN1 involves a carbocation intermediate and is favored by polar protic solvents; SN2 is a single-step mechanism favored by polar aprotic solvents.

Question 8

Which of the following compounds is most likely to undergo nucleophilic substitution via the SN1 mechanism?

Accepted Answer

Tert-butyl chloride

Question 9

In the electrophilic addition of bromine to propene in the presence of chloride ion, a mixture of two compounds is produced. What is the major reason for this?

Accepted Answer

Chloride ion acts as a nucleophile and opens the bromonium ion intermediate, leading to two products.

Question 10

Which of the following best explains why nucleophilic substitution of bromide in aliphatic compounds is more difficult than in aromatic compounds with a chloromethylbenzene derivative?

Accepted Answer

Aromatic compounds stabilize the transition state via resonance, making substitution easier.

Question 11

Which of the following is the correct order of reactivity for nucleophilic substitution (SN2) reactions?

Accepted Answer

$$CH_3Cl \u003e CH_3CH_2Cl \u003e (CH_3$)_2CHCl \u003e (CH_3$)_3CCl$$

Question 12

Which of the following is the correct order of bond strength for the following halides: H-F, H-Cl, H-Br, H-I?

Accepted Answer

$$H-F \u003e H-Cl \u003e H-Br \u003e H-I$$

Question 13

Which of the following compounds is the fastest in the SN2 mechanism reaction?

Accepted Answer

$$CH_3CH_2Cl$$

Question 14

Which of the following is the correct order of reactivity for the SN1 mechanism?

Accepted Answer

$$(CH_3$)_3CCl \u003e (CH_3$)_2CHCl \u003e CH_3CH_2Cl \u003e CH_3Cl$$

Question 15

Which of the following is the correct order of leaving group stability in the nucleophilic substitution reaction (SN2)?

Accepted Answer

$$Br^- \u003e Cl^- \u003e F^-$$

Question 16

Which of the following is the correct order of the rate of bromine addition to the double bond for the following compounds: ethylene, internal alkyne, terminally substituted alkene, conjugated diene?

Accepted Answer

Ethylene \u003e conjugated diene \u003e terminally substituted alkene \u003e internal alkyne

Question 17

Which of the following is the correct description of the reaction of $$H_2O^+$$ with propene?

Accepted Answer

Electrophilic addition forming a carbocation intermediate followed by nucleophilic attack by water.

Question 18

Which of the following is the correct order of stability for the hydrocarbon radical formed: $$CH_3$$^\cdot$$, CH_2CH_2$$^\cdot$$, CH_3CH$$^\cdot $$CH_3$$, $$C_6H_5CH_2^\cdot$$?

Accepted Answer

$$C_6H_5CH_2^\cdot \u003e CH_3CH^\cdot CH_3$ \u003e CH_2CH_2^\cdot \u003e CH_3$^\cdot$$

Question 19

Which of the following is the fastest in the SN2 mechanism reaction: $$CH_3CH_2Cl$$, $$CH_3CHClCH_3$$, $$CH_3CCl_2CH_3$$, $$CCl_4$$?

Accepted Answer

$$CH_3CH_2Cl$$

Comprehensive Study Guide: Organic Chemistry Reaction Mechanisms, Substitution, and Elimination

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