Deck 13: Dienes and the Allyl System: 2p Orbitals in Conjugation

Question 1

Which of the following structures is a ketene?

A) I
B) II
C) III
D) IV
E) V

Answer 1

II

Question 2

From left to right, what is the approximate hybridization of the indicated carbons in the structure shown here?

A)
B)
C)
D)
E)

Answer 2

Question 3

Which of the following compounds is the thermodynamic product of the reaction shown here?

A)
B)
C)
D)
E)

Answer 3

Question 4

When 1,3 -butadiene reacts with chlorine, a 50/50 mixture of 3,4 -dichloro-1-butene and (E)-1,4-dichloro-2-butene is generated. When the same diene is reacted with bromine, the 3,4 -dibromo-1-butene is the predominant product.. What could explain the difference in regioselectivity?

A) The more stable intermediate bromonium ion favors 1,2 -addition.
B) The more reactive bromide anion favors the kinetic product.
C) The more reactive chloride anion favors the thermodynamic product.
D) The more stable intermediate chloronium ion favors the 1,4 -addition product.
E) The electronegative bromine destabilizes the positive charge on the β-carbon.

Question 5

Which of the following molecules contains the most acidic hydrogen?

A) I
B) II
C) III
D) IV
E) V

Question 6

How many nodes are there in the highest energy molecular orbital for 1,3,5 -hexatriene?

A) 0
B) 2
C) 3
D) 5
E) 6

Question 7

Which of the following statements about the reaction shown here is true?

A)The major product under kinetic conditions is the 1,2 addition product because of the stability of the carbocation intermediate in that pathway.
B)The major product under kinetic conditions is the 1,2 addition product because of proximity effects.
C)The major product under kinetic conditions is the 1,4 addition product because of the stability of the carbocation intermediate in that pathway.
D)The major product under kinetic conditions is the 1,4 addition product because of proximity effects.
E)Neither carbocation stability nor proximity effects play a role in determining the preferred product under kinetic conditions.

Question 8

Which of these statements about thermodynamic and kinetic control is true?

A)The thermodynamic product is always different from the kinetic product.
B)Reactions under equilibrium conditions will favor the thermodynamic product.
C)A higher-energy transition state will favor the thermodynamic product.
D)The kinetic product will generally be favored at higher temperatures.
E)1,4-Addition gives the thermodynamic product because the intermediate cation is more stable.

Question 9

Which structure contains the longest C-C bond?

A)
B)
C)
D)
E)

Question 10

Which of the structures shown is in the s-cis conformation?

A)
B)
C)
D)
E)

Question 11

Rank these dienes in order of increasing heats of hydrogenation.

A)
B)
C)
D)
E)

Question 12

Which of the structures shown is in the s-trans conformation?

A)
B)
C)
D)
E)

Question 13

Which of the following structures is the product of 1,2 addition of HCl to the molecule shown here?

A) 4-chloro-2-methyl-1-hexene
B) 4-chloro-3-methyl-2-hexene
C) 3 -chloro-3-methyl-1-hexene
D) 5 -chloro-3-methyl-2-hexene
E) none of these

Question 14

Which of these structures is a conjugated diene?

A) I and III
B) I, III, V
C) II and IV
D) II, IV, V
E) All of these structures are conjugated dienes

Question 15

Which of these alkynes will not isomerize in the presence of NaNH₂ ?

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

Question 16

In the rearrangement of 2-butyne to 1-butyne, what causes the reaction to go to completion?

A) the increased stability of the terminal triple bond in the product
B) the high pK_a of ammonia versus the methyl group in 2-butyne
C) the decreased activation energy for conversion of the allene intermediate to 1 -butyne
D) the much lower pK_a of the acetylenic proton in the product versus the other species
E) the increased stability of the 1,2 -butadiene intermediate versus 2 -butyne

Question 17

Which of these structures is the product of 1,4 addition of HBr to the molecule shown here?

A)
B)
C)
D)
E)

Question 18

Which of these compounds can exist as cis/trans isomers?

A) I
B) II
C) III
D) IV
E) none

Question 19

Rank the following C₄H₆ isomers in order of increasing ΔH_f values:

A)
B)
C)
D)
E)

Question 20

Which of the following structures is chiral?

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

Question 21

Draw a mechanism for the formation of the product resulting from 1,4 addition of HCl to the
molecule shown here.Include all lone pairs of electrons, curved arrows, and formal charges.

Question 22

Draw the product of 1,2 addition of Br₂ to the molecule shown here.

Question 23

Which of the following molecules could not be made using a Diels-Alder reaction?

A)
B)
C)
D)
E)

Question 24

Which of the following structures is the dienophile used to make the molecule shown here?

A)
B)
C)
D)
E)

Question 25

Which of the following compounds could be classified as terpenes?

A) I and II
B) II and III
C) II and IV
D) III and IV
E) All can be classified as terpenes.

Question 26

Which of the following structures is the product of the reaction shown here?

A)
B)
C)
D)
E)

Question 27

Which of the following structures represents the basic steroid ring system?

A)
B)
C)
D)
E)

Question 28

Draw the product of 1,4 addition of Cl₂ to the molecule shown here.

Question 29

Draw a mechanism for the isomerization of the starting material to the product shown using the reagents given.

Question 30

Rate the following three C₇H₁₂ isomers from lowest to highest enthalpy of hydrogenation.

Question 31

Draw a mechanism for the formation of the product resulting from 1,2 addition of HBr to the
molecule shown here.Include all lone pairs of electrons, curved arrows, and formal charges.

Question 32

Rank the following isomers in order of increasing heats of formation.

Question 33

Which of the following dienes could react with acrylonitrile in a Diels-Alder reaction?

A)
B)
C)
D)
E)

Question 34

Which of these structures is isoprene?

A)
B)
C)
D)
E)

Question 35

Which pairing of diene and dienophile would lead to the product shown here?

A)
B)
C)
D)
E)

Question 36

Which of the following compounds gives only one constitutional isomer when it undergoes solvolysis in water? (You may ignore stereochemistry for the purposes of this question.)

A)
B)
C)
D)
E)

Question 37

Which of these orbitals is the HOMO in the allyl anion?

A)
B)
C)
D)
E)

Question 38

Which of the following statements about the Diels-Alder reaction is true?

A)The endo product is kinetically favored.
B)The exo product is kinetically favored.
C)The endo product is more stable.
D)The exo product is more stable.
E)both a and d

Question 39

Which of the following words best describes the major product(s) of the following reaction?

A) structural isomers
B) a single compound
C) racemic mixture
D) diastereomers
E) an unequal mixture of enantiomers

Question 40

Which of the following do you expect to react fastest in an reaction with cyanide ion?

A)
B)
C)
D)
E)

Question 41

Which molecular orbitals are involved in each reactant in the Diels-Alder reaction?

Question 42

Draw the lettered intermediates and products in the following synthetic sequence.Indicate the correct stereochemistry as needed.

Question 43

Provide the structures of the diene and the dienophile that were combined in a Diels-Alder reaction to form the structure shown.

Question 44

Draw the endo product of the Diels-Alder reaction shown here.

Question 45

Draw the structures of the diene and dienophile used to synthesize the product shown here.

Question 46

For each pair of reactions, indicate which would proceed at the faster rate.

Question 47

Draw the major product in the following reaction.

Question 48

Draw the product of the reaction shown here.

Question 49

Draw the products of the addition reaction under each of the conditions shown; indicate the major and minor product isomers in each case:

Question 50

Draw a mechanism for the reverse Diels-Alder reaction that occurs when the following molecule
is heated.

Question 51

Draw the kinetic and thermodynamic products of the following reaction.Indicate the general
conditions required to form each.

Question 52

Draw the structure of the product formed when cyclopentadiene dimerizes in a Diels-Alder
reaction.

Question 53

Draw a mechanism for the transformation shown here.Include all lone pairs of electrons, curved arrows, and formal charges.

Question 54

Draw the exo product of the Diels-Alder reaction shown here.

Question 55

Predict the product of the following reaction and draw an arrow-pushing mechanism for its formation.Include all lone pairs, curved arrows, and formal charges.

Question 56

Estimate the enthalpy change for the reaction shown here using the bond dissociation energies
given.

Question 57

Draw a mechanism for the transformation shown here.Include all lone pairs of electrons, curved arrows, and formal charges.

Question 58

Devise a multistep synthesis for the following transformation.You may use any organic or inorganic reagents of your choice.Include the reagents necessary for each step and the product of each step.

Question 59

S_N1 solvolysis of each of the two bromoalkenes shown gives the same mixture of two alcohols. Draw the two alcohol products and indicate which would be the major and minor isomers.

Question 60

Explain the difference between the two following molecules in their S_N2 reactivity with hydroxide ion.

Question 61

Draw the structures of the diene and dienophile used to synthesize the molecule shown here using a
Diels-Alder reaction.

Question 62

Identify the isoprene units in this structure.

Question 63

Devise a multistep synthesis for the following transformation.You may use any organic or inorganic reagents of your choice.Include the reagents necessary for each step and the product of each step.

Question 64

Convert the structure shown here to a bond-line formula showing appropriate stereochemistry at
all asymmetric carbons.

Question 65

Devise a multistep synthesis for the following transformation.You may use any organic or inorganic reagents of your choice.Include the reagents necessary for each step and the product of each step.

Question 66

The molecule shown here can undergo an intramolecular Diels-Alder reaction.Draw the product of this reaction.

Question 67

Identify the isoprene units in this structure.

Question 68

Draw the products of the reaction shown here, including stereochemistry.