Deck 9: The Chemistry of Alkyl Halides

Question 1

Consider the reaction:
a. On the left side of the equation, draw the curved-arrow notation for the reaction in the left-to-right direction.
b. On the left side of the equation, circle the nucleophile and label it "N."
c. On the left side of the equation, circle the electrophilic atom and label it "E."
d. On the left side of the equation, circle the leaving group and label it "LG."

Answer 1

Question 2

(a) Provide the structure of the missing starting material. (b) Then, assuming the reaction occurs via an S_N2 mechanism, provide the rate law using the appropriate concentration terms.

Answer 2

(b) By definition, the S_N2 reaction is a bimolecular process, and the rate law contains concentration terms for both the alkyl halide and the nucleophile.

Question 3

The rate law for this reaction is shown. Draw a circle around the alkyl halide that would have the highest value for the rate constant, k. underline the alkyl halide with the lowest value for k.

Answer 3

Question 4

Circle all possible products for the reaction:
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Question 5

Circle the reasonable mechanisms that these reactions will follow. (There may be more than one.)

Question 6

Complete the S_N2 reaction on (R)-2-iodobutane and clearly depict any stereochemistry.

Question 7

Rank the compounds in order of greatest reactivity to the S_N2 reaction, where 1 is the most reactive and 4 is the least reactive.

Question 8

What are the two products that form during an E2 reaction on (1-bromoethyl)-cyclohexane?

A) compound A
B) compound B
C) compound C
D) compound D

Question 9

Write the mechanism of the reaction (that is, S_N2, S_N1, E2, E1) that is required to form each product in the reaction:

Question 10

Give the structure of the nucleophile that would give the product shown in the S_N2 reaction. Show any charges or unshared valence electrons. Then give the curved-arrow notation for the reaction. (Show it on the diagram.)

Question 11

Under what conditions would the reaction be most likely to proceed to the product shown at a reasonable rate? (Select one.)

A) in a hydrocarbon solvent such as hexane
B) in ethanol solvent
C) in an ethanol solvent containing some water
D) in very dry dimethyl sulfoxide (DMSO, a polar aprotic solvent) containing a K⁺-bonding crown ether
E) in dimethyl sulfoxide containing a trace of water and a K⁺-bonding crown etherf.
in water containing enough acetone to dissolve the alkyl halide, plus a K⁺-bonding crown ether

Question 12

Which compound will undergo the fastest S_N1/E1 reaction in methanol, a protic solvent?

A) compound A
B) compound B
C) compound C
D) compound D
E) compound E

Question 13

Write the two possible -elimination products formed in the reaction:

Question 14

Predict the organic product(s) of the reaction and give the shorthand for mechanism (that is, E1, E2, S_N1, S_N2) by which each is formed.

Question 15

According to the rate law for the S_N2 reaction, doubling the nucleophile concentration (without changing the concentration of the electrophilic compound) should (select one)

A) decrease the reaction rate.
B) increase the reaction rate by a factor of √2.
C) increase the reaction rate by a factor of 2.
D) increase the reaction rate by a factor of 2², or 4.
E) increase the reaction rate by some other factor.

Question 16

When we say, "sodium ethoxide (Na⁺ EtO⁻) acts as a nucleophile," we always mean

A) that the sodium ion accepts a pair of electrons from the electrophile.
B) that the oxygen donates a pair of electrons to a carbon atom.
C) that the oxygen donates a pair of electrons to a leaving group.
D) that the oxygen donates a pair of electrons to an electrophile other than hydrogen.
E) that the leaving group donates a pair of electrons to the electrophile.

Question 17

Which compound will be most reactive in the S_N2 reaction with EtO⁻ Na⁺ in EtOH?

A) CH₃CH₂Br
B) (CH₃)₂CHBr
C) (CH₃)₃CCH₂Br
D) (CH₃)₃CBr
E) CH₃CH₂I

Question 18

Consider this reaction:
Draw the structures of the two -elimination products that can be formed in this reaction.

Question 19

Which species would act as the best (most reactive) nucleophile toward methyl iodide in a polar aprotic solvent?

A) compound A
B) compound B
C) compound C
D) compound D
E) compound E

Question 20

Give the two organic products of the reaction. (Ignore stereochemistry.)

Question 21

Which compound undergoes the fastest S_N2 reaction with Na⁺ CH₃O⁻?

A) CH₃CH₂Cl
B) (CH₃)₂CHCH₂Br
C) (CH₃)₃CBr
D) CH₃CH₂Br
E) CH₃CH₂F

Question 22

Which compound undergoes the fastest S_N1 solvolysis reaction with water in acetone?

A) CH₃CH₂Cl
B) (CH₃)₂CHCH₂Br
C) (CH₃)₃CBr
D) CH₃CH₂Br
E) CH₃CH₂F

Question 23

Which of these compounds will undergo the most rapid solvolysis reaction in methanol? (No base is added.)

A) compound A
B) compound B
C) compound C
D) compound D

Question 24

Rank the starting materials in terms of their rate of product formation in a reaction with sodium fluoride in dimethylformamide (1 being the fastest and 5 being the slowest). (Dimethylformamide (DMF) is a polar aprotic solvent.)
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Question 25

Rank these starting materials on their rate of reaction in hot ethanol (1 being the fastest and 4 being the slowest).