Deck 17: Conjugated Pi Systems and Pericyclic Reactions

Question 1

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

Answer 1

CH₃CH=C=CHCH₂CH₃

Question 2

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

Answer 2

2

Question 3

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

Answer 3

0

Question 4

Predict the product for the following reaction.

Question 5

Rank the following dienes in order of decreasing heat of hydrogenation (most to least).

Question 6

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 7

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

A)IB)IIIC)IVD)IIE)I

Question 8

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

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

Question 9

Rank the following dienes in order of decreasing heat of hydrogenation (most to least).

Question 10

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

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

Question 11

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

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

Question 12

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 13

Predict the product for the following reaction.

Question 14

Which one of the following dienes is most stable?

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

Question 15

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

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

Question 16

Which one of the following dienes is least stable?

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

Question 17

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 18

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 19

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

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

Question 20

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

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

Question 21

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 22

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

Question 23

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 24

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

Question 25

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 26

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

Question 27

Predict the major product for the following reaction.

Question 28

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 29

Predict the possible major products for the following reaction.

Question 30

Predict the product(s)for the following reaction.

Question 31

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 32

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 33

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

Question 34

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 35

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 dieneophile favor product formation.

Question 36

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 37

Predict the major product for the following reaction.

Question 38

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 39

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

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

Question 40

Predict the major product for the following reaction.

Question 41

Which is the most energetically favorable UV transition for 1,3-butadiene?.

A)n $\rightarrow$ $\sigma$ *
B)n $\rightarrow$ $\pi$ *
C). $\pi$ ₂ $\rightarrow$$\pi$ ₃*
D). $\sigma$ $\rightarrow$ $\sigma$ *
E). $\pi$ ₁ $\rightarrow$$\pi$ ₄*

Question 42

Which of the following compound(s)have the longest $\lambda$ _max?

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

Question 43

Which of the following compound(s)have the longest $\lambda$ _max?

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

Question 44

Absorption of UV-visible radiation by a molecule results in___________ transitions.

A)electronic
B)nuclear
C)rotational
D)vibrational
E)None of these

Question 45

Which of the following compound(s)have the longest $\lambda$ _max?

A)(E)2-pentene
B)(Z)2-pentene
C).1-pentene
D).1,3-hexadiene
E).1,3,5-hexatriene