Deck 13: Conjugated Unsaturated Systems

Question 1

Which free radical would be most stable?

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

Answer 1

III

Question 2

What product(s)would you expect from the following substitution reaction?

A) I
B) II
C) III
D) IV
E) More than one of the above

Answer 2

More than one of the above

Question 3

Which hydrogen atom(s)of is/are least susceptible to abstraction by free radicals?

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

Answer 3

III

Question 4

The allyl radical has how many electrons in non-bonding $\pi$ molecular orbitals?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 5

The allyl radical has how many bonding $\pi$ molecular orbitals?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 6

The HOMO of the allylic cation has how many electrons in its ground state?

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

Question 7

Which hydrogen atom(s)of is/are most susceptible to abstraction by free radicals?

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

Question 8

Which set of conditions does not result in allylic halogenation of an alkene?

A) Cl₂ at 400 $\degree$ C
B) Cl₂ in CCl₄ at 25 $\degree$ C
C) Cl₂,ROOR,h $\nu$
D) Br₂ at low concentration in CCl₄
E) N-Bromosuccinimide in CCl₄,ROOR

Question 9

The allyl radical has how many electrons in bonding $\pi$ molecular orbitals?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 10

The LUMO of the allylic radical has how many electrons in its ground state?

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

Question 11

What product(s)would you expect from the following substitution reaction of ¹⁴C-labeled propene?

A) "¹³CH₂=CH-CH₂Cl alone"
B) "¹³CH₂=CH-CH₂Cl and CH₂=CH-¹³CH₂Cl,in equal amounts"
C) "CH₂=CH-¹³CH₂Cl alone"
D) "more ¹³CH₂=CHCH₂Cl,but a little CH₂=CH-¹³CH₂Cl"
E) "more CH₂=CH-¹³CH₂Cl,but a little ¹³CH₂=CHCH₂Cl"

Question 12

Which carbon of is predicted to be the major site of substitution when this alkene reacts with chlorine at 400 $\degree$ C?

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

Question 13

The allyl radical has how many $\pi$ molecular orbitals?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 14

What product(s)would you expect from the following substitution reaction of ¹⁴C-labeled propene?

A) "¹⁴CH₂=CH-CH₂Cl alone"
B) "¹⁴CH₂=CH-CH₂Cl and CH₂=CH-¹⁴CH₂Cl,in equal amounts
C) CH₂=CH-¹⁴CH₂Cl alone"
D) "more ¹⁴CH₂=CHCH₂Cl,but a little CH₂=CH-¹⁴CH₂Cl"
E) "more CH₂=CH-¹⁴CH₂Cl,but a little ¹⁴CH₂=CHCH₂Cl"

Question 15

Which free radical would be most stable?

A)

B)

C)

D)

E)

Question 16

The HOMO of the allylic radical has how many electrons in its ground state?

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

Question 17

Which would be the best synthesis?

A)

B)

C)

D)

E)

Question 18

Which hydrogen atom(s)of is/are most susceptible to abstraction by free radicals?

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

Question 19

Which of the following compounds is not formed as a result of a chain-termination step in the free radical chlorination of propene?

A) CH₂=CHCH₂Cl
B) Cl₂
C) CH₂=CHCH₂CH₂CH=CH₂
D) HCl
E) All can be formed in chain-termination steps.

Question 20

Which free radical would be least stable?

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

Question 21

The allyl cation has how many electrons in bonding $\pi$ molecular orbitals?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 22

The allyl cation has how many $\pi$ molecular orbitals?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 23

Treatment of 2-butene (cis or trans)with Cl₂ at 400 $\degree$ C would yield mainly:

A) CH₂ClCHClCH₂CH₃
B) CH₃CHClCH₂CH₃
C) CH₃CH=CClCH₃
D) CH₃CH=CHCH₂Cl and CH₃CHClCH=CH₂
E) CH₃CHClCHClCH₃

Question 24

Which is not a proper resonance structure for 1,3-butadiene?

A) CH₂=CH-CH=CH₂
B)

C)

D)

E) All are correct

Question 25

The allyl cation has how many bonding $\pi$ molecular orbitals?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 26

An unsaturated product results from the reaction of cyclohexene with which of these?

A) Br₂/CCl₄ at 25 $\degree$ C
B) NBS/CCl₄,ROOR
C) HCl,ROOR
D) HCl,no peroxides
E) More than one of these

Question 27

Arrange these carbocations in order of expected increasing stability.

A) V < II < I < IV < III
B) VC) IV D) IV < III < I < II < V
E) I < II < IV < III < V

Question 28

What is (are)the product(s)of the following reaction?

A) I
B) II
C) III
D) a mixture of I and II
E) a mixture of II and III

Question 29

What product(s)would you expect from the following substitution reaction of ¹⁴C-labeled propene?

A) "¹⁴CH₂=CH-CH₂Br alone"
B) "¹⁴CH₂=CH-CH₂Br and CH₂=CH-¹⁴CH₂Br in equal amounts
C) CH₂=CH-¹⁴CH₂Br alone"
D) "More ¹⁴CH₂=CHCH₂Br but a little CH₂=CH-¹⁴CH₂Br"
E) "More CH₂=CH¹⁴CH₂Br but a little ¹⁴CH₂=CHCH₂Br"

Question 30

Which carbocation would be least stable?

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

Question 31

Which is not an example of resonance?

A) I
B) II
C) III
D) IV
E) None of these are examples of resonance.

Question 32

Treatment of 2-butene (cis or trans)with N-bromosuccinimide in CCl₄ would yield mainly:

A) CH₃CHBrCHBrCH₃ alone
B) CH₃CH=CBrCH₃ alone
C) CH₃CH=CHCH₂Br alone
D) CH₂BrCH₂CH=CH₂ and CH₃CH=CHCH₂Br
E) CH₃CHBrCH=CH₂ and CH₃CH=CHCH₂Br

Question 33

Which of the following could be used to synthesize 3-bromopropene?

A)

B)

C) CH₂=CHCH₂OH + PBr₃ $\rightarrow$
D) More than one of these
E) None of these

Question 34

Which carbocation would be most stable?

A)

B)

C)

D)

E)

Question 35

Which carbocation would be most stable?

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

Question 36

Which pair does not represent a pair of resonance structures?

A) I
B) II
C) III
D) IV
E) All of these represent pairs of resonance structures.

Question 37

Which pair does not represent a pair of resonance structures?

A) I
B) II
C) III
D) IV
E) All of these represent pairs of resonance structures.

Question 38

Which carbocation would be most stable?

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

Question 39

Which pair does not represent a pair of resonance structures?

A) I
B) II
C) III
D) IV
E) All of these represent pairs of resonance structures.

Question 40

Treatment of 4-methylcyclohexene with N-bromosuccinimide in CCl₄ would yield mainly:

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

Question 41

The HOMO of 1,3-pentadiene has how many electrons in its ground state?

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

Question 42

Which pair does not represent a pair of resonance structures?

A) I
B) II
C) III
D) IV
E) All of these represent pairs of resonance structures.

Question 43

Select the structure of the conjugated diene.

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

Question 44

Which carbon-carbon bond in the following compound would you expect to be longest?

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

Question 45

Which of the following compounds would be the most stable?

A) I
B) II
C) III
D) IV
E) They are all of equal stability.

Question 46

Select the structure of the conjugated diene.

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

Question 47

Select the structure of the conjugated diene.

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

Question 48

What is an IUPAC name for

A) 2,3-methylhept-2-en-4-yne
B) 1,1,3-trimethylhex-3-yn-1-ene
C) 1,1,3-trimethyl-3-hexyn-1-ene
D) 2,3-dimethyl-2-hepten-4-yne
E) 5,6-dimethyl-5-hepten-3-yne

Question 49

Which of the following dienes is a cumulated diene?

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

Question 50

The LUMO of 1,3-pentadiene has how many electrons in its excited state?

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

Question 51

Which of the following dienes is a cumulated diene?

A) CH₂=CHCH₂CH₂CH₂CH=CH₂
B) CH₂=CHCH=CHCH₂CH₂CH₃
C) CH₃CH=C=CHCH₂CH₂CH₃
D) CH₃CH=CHCH=CHCH₂CH₃
E) CH₃CH₂CH=CHCH₂CH=CH₂

Question 52

Which carbon-carbon bond in the following compound would you expect to be shortest?

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

Question 53

Which of the following dienes would you expect to be the 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 54

Which compound would have the shortest carbon-carbon single bond?

A) CH₃-CH₃
B) CH₂=CH-CH₃
C) HC $\equiv$ C-C $\equiv$ CH
D) CH₂=CH-C $\equiv$ CH
E) CH₂=CH-CH=CH₂

Question 55

What is an IUPAC name for this triene?

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

Question 56

What is an IUPAC name for this triene?

A) (2E,4Z,6E)-2,4,6-Nonatriene
B) (2Z,4E,6Z)-2,4,6-Nonatriene
C) (2E,4Z,6Z)-2,4,6-Nonatriene
D) (3Z,5Z,7E)-3,5,7-Nonatriene
E) (3Z,5E,7E)-3,5,7-Nonatriene

Question 57

The LUMO of 1,3-pentadiene has how many electrons in its ground state?

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

Question 58

Select the structure of the isolated diene.

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

Question 59

The HOMO of 1,3-pentadiene has how many electrons in its excited state?

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

Question 60

Which of the following dienes would you expect to be the most stable?

A) CH₃CH₂CH=CHCH₂CH=CHCH₃
B) CH₃CH=CHCH=CHCH₂CH₃
C) CH₂=CHCH₂CH₂CH₂CH=CH₂
D) CH₂=CHCH=CHCH₂CH₂CH₃
E) CH₃CH₂CH=C=CHCH₂CH₃

Question 61

Which alkene would you expect to have the highest heat of hydrogenation?

A)

B)

C)

D)

E)

Question 62

Which of the following dienes would you expect to be the least stable?

A) CH₃CH₂CH=CHCH₂CH=CHCH₃
B) CH₃CH=CHCH=CHCH₂CH₃
C) CH₂=CHCH₂CH₂CH₂CH=CH₂
D) CH₂=CHCH=CHCH₂CH₂CH₃
E) CH₃CH=C(CH₃)CH=CHCH₂CH₃

Question 63

Estimate the stabilization energy for 1,3-cyclohhexadiene using the heats of hydrogenation in Table 1. Table 1.
Heats of Hydrogenation for Selected Compounds
Compound
Moles H₂
$\Delta$ H(kJ mol^-1)
Cyclohexene
1
-120
1,4-Cyclohexadiene
2
-240
1,3-Cyclohexadiene
2
-232
1,5-Hexadiene
2
-253

A) 13 kJ mol^-1
B) 21 kJ mol^-1
C) 8 kJ mol^-1
D) 120 kJ mol^-1
E) 112 kJ mol^-1

Question 64

Which alkene would you expect to be most stable?

A) CH₂=CHCH₂CH₂CH=CH₂
B)

C)

D)

E)

Question 65

Which alkene would you expect to have the smallest heat of hydrogenation?

A)

B)

C)

D)

E)

Question 66

Select 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 67

Considering both configurational and conformational factors,select the most stable form of 2,4-hexadiene.

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

Question 68

Ignoring stereochemistry,the 1:1 reaction of bromine with 1,3-cyclohexadiene at 25 $\degree$ C in the dark and in the absence of peroxide forms which of these?

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

Question 69

Arrange these hexadienes in order of expected increasing stability.

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

Question 70

Which of the following dienes would you expect to be the most stable?

A) CH₃CH₂CH=CHCH₂CH=CHCH₃
B) CH₃CH=CHCH=CHCH₂CH₃
C) CH₂=CHCH₂CH₂CH₂CH=CH₂
D) CH₂=CHCH=CHCH₂CH₂CH₃
E) CH₃CH=C(CH₃)CH=CHCH₂CH₃

Question 71

Considering both configurational and conformational factors,select the least stable form of 2,4-hexadiene.

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

Question 72

Estimate the stabilization energy for 1,3-pentadiene using the heats of hydrogenation in Table 1. Table 1.
Heats of Hydrogenation for Selected Compounds
Compound
Moles H₂
$\Delta$ H(kJ mol^-1)
1-Butene
1
-127
1-Pentene
Trans-2-pentene
1
1
-126
-115
1,3-Butadiene
2
-239
Trans-1,3-Pentadiene
2
-226

A) 13 kJ mol^-1
B) 15 kJ mol^-1
C) 28 kJ mol^-1
D) 239 kJ mol^-1
E) 112 kJ mol^-1

Question 73

Which of these symbols is used in connection with the intensity of absorption in the UV-visible region?

A) " $\infty$ "
B) " $\nu$ "
C) " $\varepsilon$ "
D) " $\lambda$ "
E) " $\theta$ "

Question 74

Which compound would have a UV absorption band at longest wavelength?

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

Question 75

Which alkene would you expect to have the lowest heat of hydrogenation?

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

Question 76

Which alkene would you expect to have the smallest heat of hydrogenation?

A) CH₂=CHCH₂CH₂CH=CH₂
B)

C)

D)

E)

Question 77

Arrange these hexadienes in order of expected decreasing stability.

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

Question 78

Which of the following dienes might react with bromine in CCl₄ to yield 2,5-dibromo-3-hexene?

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

Question 79

Which compound would have a UV absorption band at longest wavelength?

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

Question 80

Estimate the stabilization energy for 1,3-butadiene using the heats of hydrogenation in Table 1. Table 1.
Heats of Hydrogenation for Selected Compounds
Compound
Moles H₂
$\Delta$ H(kJ mol^-1)
1-Butene
1
-127
1-Pentene
1
-126
1,3-Butadiene
2
-239
Trans-1,3-Pentadiene
2
-226

A) 13 kJ mol^-1
B) 15 kJ mol^-1
C) 28 kJ mol^-1
D) 239 kJ mol^-1
E) 112 kJ mol^-1