Deck 5: Structure and Preparation of Alkenes: Elimination Reactions

Question 1

Carbon-carbon double bonds do not freely rotate like carbon-carbon single bonds. Why?

A) The double bond is much stronger and thus more difficult to rotate.
B) Overlap of the two 2 p orbitals of the $\pi$ bond would be lost.
C) The shorter bond length of the double bond makes it more difficult for the attached groups to pass each other.
D) Overlap of the $\mathrm{sp}^{2}$ orbitals of the carbon-carbon $\sigma$ bond would be lost.

Answer 1

Overlap of the two 2 p orbitals of the $\pi$ bond would be lost.

Question 2

What is the IUPAC name of the following compound?

A) 2-methyl-3-propyl-2-pentene
B) 3-ethyl-2-methyl-2-hexene
C) 4-ethyl-5-methyl-4-hexene
D) 4-methyl-3-propyl-3-pentene

Answer 2

3-ethyl-2-methyl-2-hexene

Question 3

Which of the following alkenes exhibit E-Z isomerism?
I. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CHCH}_{2} \mathrm{CH}_{3}$
II. $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{CHCH}_{3}$
III. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CHBr}$
IV. $\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}$

A) I and II
B) I and III
C) II and IV
D) I, II, and III

Answer 3

I and III

Question 4

Which of the following $\mathrm{C}_{6} \mathrm{H}_{12}$ isomers has the highest heat of combustion?

A) 1-hexene
B) trans-3-hexene
C) cis-3-hexene
D) 2-methyl-2-pentene

Question 5

Identify the major organic product expected from the acid-catalyzed dehydration of 2-methyl-2pentanol.

A) 2-methyl-1-pentene
B) 2-methyl-2-pentene
C) 3-methyl-1-pentene
D) cis-3-methyl-2-pentene

Question 6

What is the slow, rate-determining step, in the acid-catalyzed dehydration of 2-methyl-2-propanol?

A) Protonation of the alcohol to form an oxonium ion.
B) Loss of water from the oxonium ion to form a carbocation.
C) Loss of a $\beta$ -hydrogen from the carbocation to form an alkene.
D) The simultaneous loss of a $\beta$ -hydrogen and water from the oxonium ion.

Question 7

Which of the following carbocations is(are) likely to undergo a rearrangement?

A) only I
B) I and III
C) II and III
D) I, II, and III

Question 8

Predict the major product of the following reaction.

A)

B)

C)

D)

Question 9

In the dehydrohalogenation of 2-bromobutane, which conformation below leads directly to the formation of cis-2-butene?

A) only I
B) only II
C) only III
D) I and II

Question 10

Which of the following cannot undergo an E2 reaction?

A) only I
B) only II
C) only III
D) I and III

Question 11

Which of the following would have the fastest rate of reaction to form 4-tert-butylcyclohexene?

A)

B)

C)

D)

Question 12

What is the first step in the mechanism of the dehydration reaction of a tertiary alcohol with sulfuric acid to form an alkene?

A) the loss of $\mathrm{OH}^{-}$ to form a carbocation
B) the protonation of the hydroxyl group
C) the loss of the proton from the hydroxyl group to give an alkoxide ion
D) the removal of a $\beta$ -hydrogen from the alcohol

Question 13

Which of the following does not give 1, 2-dimethylcyclohexene as one of the acid-catalyzed dehydration products?

A)
B)
C)
D)

Question 14

Which of the following compounds gives a single E2 product on reaction with sodium ethoxide, $\mathrm{NaOCH}_{2} \mathrm{CH}_{3}$ ?

A) I and II
B) I and III
C) II and III
D) I, II, and III

Question 15

Which of the following stereoisomers gives the exclusive E2 product shown?

A)

B)

C)

D)

Question 16

What is the major product of the reaction sequence shown below?

A) 2-methyl-1-butene
B) 2-methyl-2-butene
C) 3-methyl-1-butene
D) 2-methylbutane

Question 17

Which of the alkenes below has the Z-configuration?

A)

B)

C)

D)

Question 18

If you wanted to make compound III, starting with compound I or II, what would you do?

A) React I with $\mathrm{H}_{2} \mathrm{SO}_{4}$ .
B) React II with NaOEt.
C) Either of the reactions in A or B above would work.
D) Neither of the reactions in A or B above would work.