Deck 17: Conjugated Pi Systems and Pericyclic Reactions

Question 1

Which of the following compounds have isolated double bonds?

Answer 1

II & IV

Question 2

Classify the following compounds as having cumulated, conjugated or isolated double bonds?

Answer 2

I. CONJUGATED
II. cumulated
III. conjugated
IV. conjugated
V. isolated

Question 3

Which of the following compounds is (are) a conjugated diene(s)?

A) 4-methyl-1,3-heptadiene
B) 3-methyl-1,5-heptadiene
C) 2-methyl-2,4-heptadiene
D) 4-methyl-1,4-heptadiene
E) 5-methyl-2,3-heptadiene

Answer 3

4-methyl-1,3-heptadiene
2-methyl-2,4-heptadiene

Question 4

Which of the following compounds have conjugated double bonds?

Question 5

Dienes with adjacent $\pi$ bonds are classified as ______.

A) isolated
B) cumulated
C) skipped
D) conjugated
E) none of these

Question 6

What is the IUPAC name for the following compound?

Question 7

Which of the following compounds is an isolated diene?

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

Question 8

Dienes with $\pi$ bonds separated by two or more $\sigma$ bonds are classified as ______.

A) isolated
B) cumulated
C) skipped
D) conjugated
E) none of these

Question 9

What is the IUPAC name for the following compound?

A) 1-chloro-1-methyl-2,5-cyclohexadiene
B) 3-chloro-3-methyl-1,4-cyclohexadiene
C) 6-chloro-6-methyl-1,4-cyclohexadiene
D) 2-chloro-2-methyl-1,3-cyclohexadiene
E) None of these

Question 10

Zingiberene, a terpene found in ginger has the following structure. Classify the $\pi$ bonds in zingiberene as conjugated, cumulated or isolated.

Question 11

Which of the following compounds is (are) a isolated diene(s)?

A) 4-methyl-1,3-heptadiene
B) 3-methyl-1,5-heptadiene
C) 2-methyl-2,4-heptadiene
D) 4-methyl-1,4-heptadiene
E) 5-methyl-2,3-heptadiene

Question 12

Dienes with alternate $\pi$ and $\sigma$ bonds are classified as ______.

A) isolated
B) cumulated
C) skipped
D) conjugated
E) none of these

Question 13

What is the IUPAC name for the following compound?

A) (2E,4Z,6E)-3,4,7,8-tetramethyl-2,4,6-heptatriene
B) (2Z,4E)-3,4,7-trimethyl-2,4,6-octatriene
C) (2E,4Z,6E)-2,5,6,7-tetramethyl-3,5,7-heptatriene
D) (2E,4Z)- 2,5,6-trimethyl-3,5,7-octatriene
E) (4E,6E)-2,5,6-trimethyl-2,4,6-octatriene

Question 14

Which of the following compounds is (are) a cumulated diene(s)?

A) 4-methyl-1,3-heptadiene
B) 3-methyl-1,5-heptadiene
C) 2-methyl-2,4-heptadiene
D) 4-methyl-1,4-heptadiene
E) 5-methyl-2,3-heptadiene

Question 15

Provide the structure for (E)-1,3-pentadiene.

Question 16

Provide the structure for (Z)-2-methyl-2,4-hexadiene.

Question 17

Which of the following compounds is (are) a conjugated diene(s)?

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

Question 18

What is the IUPAC name for the following compound?

A) (2E, 4Z)-2,4-hexadiene
B) (2E, 4Z)-1,4-dimethyl-1,3-butadiene
C) (2Z, 4Z)-1,4-dimethyl-1,3-butadiene
D) (2Z, 4Z)-2,4-hexadiene
E) None of these

Question 19

Provide the structure for (1E,3Z)-1-methoxy-2-methyl-1,3-pentadiene.

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

Question 20

Vitamin D₃ has the following structure. Classify the $\pi$ bonds in vitamin D₃ as conjugated, cumulated or isolated.

Question 21

Which of the following indicated C-C bond is the longest?

A) I
B) II
C) III
D) both I& II

Question 22

Predict the product for the following reaction.

A) I
B) II
C) III
D) IV
E) both I & III

Question 23

Predict the product for the following reaction.

Question 24

Rank the indicted C-C bonds in increasing order of bond length (shortest to longest)

A) IIIB) IIC) ID) IE) II

Question 25

Rank the following dienes in order of decreasing heat of hydrogenation (highest to lowest).

Question 26

Provide the structure for (S,E)-3-t-butyl-4-methyl-1,4-hexadiene.

Question 27

Which one of the following dienes will have the highest heat of hydrogenation?

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

Question 28

Predict the product for the following reaction.

A) I
B) II
C) III
D) IV
E) both I & III

Question 29

Predict the product for the following reaction.

Question 30

Which one of the following dienes will have the lowest heat of hydrogenation?

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

Question 31

Provide the reagents necessary to carry out the following conversion.

Question 32

Which of the following indicated C-C bond is the shortest?

A) I
B) II
C) III
D) both I& II

Question 33

Which one of the following dienes is most stable?

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

Question 34

Rank the following dienes in increasing order of stability (least to most).

A) IB) IIIC) IVD) IIE) I

Question 35

Which one of the following dienes is least stable?

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

Question 36

Which one of the following dienes is least stable?

A) CH₃CH=CHCH=CHCH₃
B) CH₃CH=CHCH₂CH=CH₂
C) CH₂=CHCH₂CH₂CH=CH₂
D) CH₂=CHCH(CH₃)CH=CH₂
E) CH₃CH=C=CHCH₂CH₃

Question 37

Rank the following dienes in order of decreasing heat of hydrogenation (highest to lowest).

Question 38

Provide the reagents necessary to carry out the following conversion.

Question 39

Provide the reagents necessary to carry out the following conversion.

Question 40

Which one of the following dienes is most stable?

A) CH₃CH=CHCH=CHCH₃
B) CH₃CH=CHCH₂CH=CH₂
C) CH₂=CHCH₂CH₂CH=CH₂
D) CH₂=CHCH(CH₃)CH=CH₂
E) CH₃CH=C=CHCH₂CH₃

Question 41

Predict the major product for the following reaction.

Question 42

Which one of the following represents the highest energy $\pi$ -antibonding molecular orbital of 1,3-butadiene?

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

Question 43

A thermodynamically-controlled reaction will yield :

A) the most stable product.
B) the product whose formation requires the smallest free energy of activation.
C) the product that can be formed in the fewest steps.
D) the product that is formed at the fastest rate.
E) None of these.

Question 44

Predict the product(s) for the following reaction.

Question 45

Predict the major product for the following reaction.

Question 46

Predict the possible major products for the following reaction.

Question 47

A reaction under kinetic control will yield :

A) the most stable product.
B) the product that can be formed in the fewest steps.
C) the product whose formation requires the smallest free energy of activation.
D) the product with the greatest potential energy.
E) None of these

Question 48

How many $\pi$ -bonding molecular orbitals does 1,3-pentadiene have?

A) 1
B) 2
C) 3
D) 4
E) none

Question 49

Which major product(s) are formed for the following reaction?

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

Question 50

How many electrons does the LUMO of 2,4-hexadiene have in its ground state?

A) 1
B) 2
C) 3
D) 4
E) 0

Question 51

Predict the possible products for the following reaction and provide a curved arrow mechanism for the formation of these products.

Question 52

Which one of the following represents the lowest energy $\pi$ -bonding molecular orbital of 1,3-butadiene?

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

Question 53

Provide the structure of the 1,4 addition product for the reaction of 1,3-hexadiene with Br₂/CCl₄.

Question 54

Which one of the following compounds is not a product of reaction between 1,3-butadiene and HBr?

A) (S)-3-bromo-1-butene
B) (R)-3-bromo-1-butene
C) (E)-1-bromo-2-butene
D) (Z)-1-bromo-2-butene
E) (Z)-2-bromo-2-butene

Question 55

Which one of the following represents the LUMO of 1,3,5-hexatriene?

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

Question 56

Provide the structure of the 1,2 addition product for the following reaction.

Question 57

How many electrons does the HOMO of 1,3-pentadiene have in its excited state?

A) 1
B) 2
C) 3
D) 4
E) none

Question 58

Which one of the following represents the HOMO of 1,3,5-hexatriene?

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

Question 59

How many electrons does the HOMO of 2,4-hexadiene have in its ground state?

A) 1
B) 2
C) 3
D) 4
E) 0

Question 60

Both s-cis and s-trans conformers of 1,3-butadiene have a continuous conjugated $\pi$ system. Which of the following statements is true about the s-cis conformer?

A) The s-cis conformer is lower in energy than the s-trans conformer
B) The s-cis conformer is higher in energy than the s-trans conformer
C) The s-cis conformer has equal energy as the s-trans conformer
D) none of these

Question 61

What is the correct classification of the following pericyclic reaction?

A) electrophilic addition
B) sigmatropic rearrangement
C) cycloaddition
D) electrocyclic reaction
E) C & D

Question 62

The Diels Alder reaction is a concerted reaction, which means

A) The product contains a cyclic ring
B) The diene must be in the s-cis conformation to react.
C) All changes in bonding (bond making and bond breaking) occur simultaneously.
D) It is an endothermic reaction
E) Both exo and endo products are formed

Question 63

Predict the major product for the following Diels-Alder reaction.

Question 64

Provide the structure for 1,2 addition product for the following reaction and explain why it is a major product rather than 1,4 addition product.

Question 65

Predict the major product for the following Diels-Alder reaction.

Question 66

Which of the following dienes can undergo the Diels-Alder reaction?

A)I
B)II
C)III
D)IV
E)All of the these

Question 67

Predict the major product for the following Diels-Alder reaction.

Question 68

Predict the major product for the following Diels-Alder reaction.

Question 69

Which one of the following dienophiles is least reactive in the Diels-Alder reaction?

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

Question 70

Which of the following is true of pericyclic reactions?

A) they are concerted reactions
B) proceed via a cyclic transition state
C) no intermediates are formed
D) all of these

Question 71

The following diene does not undergo Diels Alder reaction because _____.

A) it does not have an electron donating group
B) it does not have an electron withdrawing group
C) the bicyclic ring does not function as a diene
D) it cannot adopt the s-cis conformation
E) the double bonds are not in the same cyclic ring

Question 72

Predict the major product for the following reaction and explain why it is major product.

Question 73

Predict the product for the following Diels-Alder reaction.

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

Question 74

Predict the product for the following Diels-Alder reaction.

A) I
B) II
C) III
D) IV
E) None of these

Question 75

Which one of the following dienophiles is most reactive in the Diels-Alder reaction?

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

Question 76

What is the correct classification of the following pericyclic reaction?

A) electrophilic addition
B) sigmatropic rearrangement
C) cycloaddition
D) electrocyclic reaction
E) C & D

Question 77

What is the correct classification of the following pericyclic reaction?

A) electrophilic addition
B) sigmatropic rearrangement
C) cycloaddition
D) electrocyclic reaction
E) C & D

Question 78

Which statement is NOT true about the Diels-Alder reaction?

A) It is a [4+2] cycloaddition reaction.
B) The diene must be in the s-cis conformation to react.
C) Most Diels-Alder reactions are reversible.
D) It is a sigmatropic rearrangement.
E) Electron donating groups on the diene and electron withdrawing groups on the dienophile favor product formation.

Question 79

Predict the major product for the following reaction.

Question 80

Which of the following diene(s) cannot undergo the Diels-Alder reaction?

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