Deck 20: Dienes, Conjugated Systems, and Pericyclic Reactions

Question 1

What is the correct order of exothermicity for hydrogenation of the following hexadienes upon treatment with H₂/Pd (more exothermic > less exothermic)?

A) 1 > 2 > 3
B) 3 > 1 > 2
C) 2 > 1 > 3
D) 3 > 2 > 1

Answer 1

3 > 1 > 2

Question 2

Which of the following alkenes undergoes the least exothermic hydrogenation upon treatment with H₂/Pd

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

Answer 2

3

Question 3

Which of the following is(are) formed upon addition of 1 mol of Br₂ to 1,3-cyclohexane?

A) only 2
B) only 1 and 3
C) only 2 and 4
D) 1, 2 and 3

Answer 3

only 2 and 4

Question 4

What is (are) the major organic product(s) formed in the following reaction?

A) only 1
B) only 3
C) only 1 and 3
D) only 2 and 4

Question 5

What is the IUPAC name of the following compound?

A) 2,3-dimethyl-2,4-pentadiene
B) (Z)-2,3-dimethyl-2,4-pentadiene
C) 3,4-dimethyl-1,3-pentadiene
D) (Z)-3,4-dimethyl-1,3-pentadiene

Question 6

Which of the following are conjugated dienes?

A) only 1
B) only 2
C) only 1 and 2
D) 1, 2 and 3

Question 7

Which of the following terms describes the mechanism for the addition of Br₂ to butadiene?

A) electrophilic addition
B) nucleophilic addition
C) pericyclic addition
D) conjugate addition

Question 8

What is the kinetic product obtained from the addition of 1 mole of bromine to 1,3-butadiene?

A) 3,4-dibromo-1-butene
B) (E)-1,4-dibromo-2-butene
C) (Z)-1,4-dibromo-2-butene
D) (Z)-2,3-dibromo-2-butene

Question 9

Which of the following is not a major organic product obtained from the addition of 1 mole of bromine to (E)-1,3-pentadiene?

A) (E)-4,5-dibromo-2-pentene
B) 3,4-dibromo-1-pentene
C) (E)-1,4-dibromo-2-pentene
D) (E)-1,2-dibromo-2-pentene

Question 10

What is (are) the major organic product(s) formed in the following reaction?

A) only 1
B) only 1 and 2
C) only 1 and 3
D) only 2 and 4

Question 11

What is the reactive intermediate in the reaction of 1,3-butadiene with HBr resulting in 1,2-addition?

A) cyclic bromonium cation
B) allylic cation
C) allylic radical
D) dienophile

Question 12

Which of the following arrangements of p atomic orbitals gives the highest energy π-antibonding molecular orbital of 1,3-butadiene?

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

Question 13

What is the systematic IUPAC name of the following compound?

A) (3S,4E)-3-ethyl-3,4-dimethyl-1,4-hexadiene
B) (3R,4E)-3-ethyl-3,4-dimethyl-1,4-hexadiene
C) (3S,4Z)-3-ethyl-3,4-dimethyl-1,4-hexadiene
D) (3R,4Z)-3-ethyl-3,4-dimethyl-1,4-hexadiene

Question 14

Which of the following arrangements of p atomic orbitals gives the lowest energy π-bonding molecular orbital of 1,3-butadiene?

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

Question 15

What is the thermodynamic product obtained from the addition of 1 mole of bromine to 1,3-butadiene?

A) 3,4-dibromo-1-butene
B) (E)-1,4-dibromo-2-butene
C) (Z)-1,4-dibromo-2-butene
D) (Z)-2,3-dibromo-2-butene

Question 16

What is (are) the major organic product(s) formed in the following reaction?

A) only 1
B) only 2
C) only 1 and 3
D) only 2 and 4

Question 17

Which of the following are conjugated dienes?

A) only 1
B) only 2
C) only 1 and 2
D) 1, 2 and 3

Question 18

What is (are) the major organic product(s) formed in the following reaction?

A) only 1
B) only 1 and 3
C) only 2 and 4
D) only 1 and 4

Question 19

Which of the following arrangements of p atomic orbitals of 1,3-butadiene has the greatest number of nodes?

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

Question 20

What is the IUPAC name of the following compound?

A) (R)-3-vinyl-1-butene
B) 3-methyl-1,5-pentadiene
C) 3-methyl-1,4-pentadiene
D) (R)-3-methyl-1,4-pentadiene

Question 21

Which of the following has the highest value of λ_max in the ultraviolet-visible spectrum?

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

Question 22

What are the units of λ_max in ultraviolet-visible spectroscopy?

A) J⋅mol−¹
B) M−¹
C) nm
D) none, λ_max is a dimensionless quantity

Question 23

For a diene to undergo a Diels-Alder reaction it must be able to adopt an s-trans conformation.

Question 24

Which of the following energy diagrams represents the electronic state of butadiene after absorption of radiation?

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

Question 25

Which of the following relationships is not valid as applied to ultraviolet-visible spectroscopy?

A) A = log (I_o/I)
B) A = εcl
C) ΔE = hν
D) A = λ_maxl

Question 26

The conjugated portion of the following molecule is circled.

Question 27

Electrophilic addition reaction of conjugated dienes that occur at high temperature and/or long reaction times (reversible conditions) are said to be under kinetic control.

Question 28

Which of the following processes takes place upon absorption of ultraviolet-visible radiation?

A) bond vibration
B) electron excitation
C) nuclear spin flip
D) electron spin flip

Question 29

What range of wavelengths corresponds to the ultraviolet region of the electromagnetic spectrum?

A) 200-400 nm
B) 400-700 nm
C) 2.5-25 μm
D) 2-10 mm

Question 30

Which of the following has the highest value of λ_max in the ultraviolet-visible spectrum?

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

Question 31

Which of the following reaction coordinate diagrams explains the formation of different thermodynamic (T) and kinetic products from the same reactants (R)?

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

Question 32

Consider the following structure. This substance could be produced by the reaction of the following diene and dienophile.

Question 33

The conjugated portion of the following molecule is circled.

Question 34

Which of the following energy diagrams represents the electronic state of the ground state of 1,3-butadiene?

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

Question 35

What are the units of ε in ultraviolet-visible spectroscopy?

A) M−¹⋅cm−¹
B) M⋅cm
C) J⋅mol−¹⋅M−¹
D) none, ε is a dimensionless quantity

Question 36

What quantity is abbreviated as ε in ultraviolet-visible spectroscopy?

A) absorbance
B) molecular absorptivity
C) intensity of transmitted light
D) wavelength of maximum absorbance

Question 37

Which of the following laws relates absorbance to the concentration of a sample and the pathlength in ultraviolet-visible spectroscopy?

A) Buzz-Beer law
B) Beer-Lambert law
C) Duff-Beer law
D) Christopher-Lambert law

Question 38

Which of the following electronic transitions is apparent in the ultraviolet-visible spectrum of 1,3-butadiene?

A) n → π*
B) π → π *
C) σ → π *
D) σ → π

Question 39

What is (are) the major organic product(s) formed in the following reaction?

A) only 1
B) only 2
C) only 3
D) 1, 2 and 3

Question 40

What are the units of absorbance, A, in ultraviolet-visible spectroscopy?

A) J⋅mol−¹
B) nm⋅mol−¹
C) J⋅mol−¹⋅M−¹
D) none, A is a dimensionless quantity

Question 41

Consider the following reaction. This is an example of a sigmatropic reaction with a [3,3]-shift.

Question 42

Consider the reaction below to answer the following question(s). Fill in the blank in the question with the appropriate letter.
The dienophile in the reaction is ____.

Question 43

The following spectrum could arise from π to π* transitions.

Question 44

Consider the reaction below to answer the following question(s): Enter the appropriate letter in the blank for each the following statements.
The product that results from following mechanistic step is _____.

Question 45

Consider the reaction below to answer the following question(s). Fill in the blank in the question with the appropriate letter.
This is an example of a(n) ____________ reaction.
A. sigmatropic reaction
B. electrophillic addition
C. Diels-Alder reaction
D. Cope rearrangement

Question 46

What is the IUPAC name of the following compound?

Question 47

What is the IUPAC name of the following compound?

Question 48

Consider the following spectrum for a conjugated diene. If a similar spectrum were taken for a conjugated tetraene, the λ_max would be _________than 217 nm.

Question 49

Based on the following table.

Compound ______ has the largest energy difference between the HOMO and LUMO.

Question 50

The following compound could act as a diene in a Diels-Alder reaction.

Question 51

Sigmatropic shifts, cycloaddition reactions and anuulation reactions are all examples of pericyclic reactions.

Question 52

The following two compounds could be easily distinguished by NMR, IR, UV or MS spectra.

Question 53

Consider the following reaction. This is an example of a sigmatropic reaction with a [3,3]-shift.

Question 54

For Diels-Alder cycloaddition reactions to take place most rapidly and in highest yield a dienophile must be substituted with electron-donating groups.

Question 55

Consider the reaction below to answer the following question(s): Enter the appropriate letter in the blank for each the following statements.
The electrophile in this reaction is ____.

Question 56

Consider the reaction below to answer the following question(s). Fill in the blank in the question with the appropriate letter.
The diene in the reaction is ____.

Question 57

Consider the reaction below to answer the following question(s): Enter the appropriate letter in the blank for each the following statements.
The nucleophile in this reaction is ____.

Question 58

Consider the reaction below to answer the following question(s): Enter the appropriate letter in the blank for each the following statements.
The product that results from 1,4-addition is _____.

Question 59

Consider the reaction below to answer the following question(s): Enter the appropriate letter in the blank for each the following statements.
The kinetically controlled product in this reaction is _____.

Question 60

When an organic molecule is irradiated with ultraviolet radiation, the energy absorbed by the molecule corresponds to the amount necessary to excite electrons from one molecular orbital to another.

Question 61

Provide the structures of the constitutional isomers of the two major organic products obtained from the following reaction?

Question 62

What are the two major organic products obtained from the following reaction?

Question 63

Why carbonyl groups of aldehydes and ketones on conjugation with carbon-carbon double bonds show strong absorption in the ultraviolet spectrum?

Question 64

The molar absorptivity of ethylene in hexane is 15,000 L mol⁻¹ cm⁻¹. What is the maximum absorbance observed at a concentration of 1.5 x 10⁻⁴ mol L⁻¹? (Path length = 1 cm)

A) 2.25
B) 1.25
C) 3.25
D) 2.52

Question 65

Which of 1,3-cyclohexadiene and 1,4-cyclohexadiene has the greatest heat of hydrogenation (i.e., the most exothermic reaction with H₂ in the presence of a catalyst). Provide a brief explanation for your choice ?

Question 66

What is the major organic product obtained from the following reaction?

Question 67

The [2+2] cycloaddition reaction of ethylene to form cyclobutane does not occur because _____. ​

A) the reaction is forbidden as determined by the frontier molecular orbital analysis
B) the reaction is allowed as determined by the frontier molecular orbital analysis
C) the reaction is allowed, and ethylene collides in a suprafacial manner
D) the reaction is allowed, and ethylene collides in an antarafacial manner

Question 68

How would you be able to distinguish between 1,3-cyclohexadiene and 1,4-cyclohexadiene using ultraviolet spectroscopy?

Question 69

What are the two major organic products obtained from the following reaction?

Question 70

Draw two resonance structures of the reactive intermediate that accounts for the formation of 1,2- and 1,4-addition products upon reaction of 1,3-butadiene with one equivalent of HBr.

Question 71

Pericyclic reactions occur in a single step with the _____.

A) formation of a radical
B) formation of an ionic intermediate
C) formation of a molecular ion
D) formation of a transition state

Question 72

Identify the product of the given reaction. ​

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

Question 73

Identify the product of the given reaction. ​

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

Question 74

Draw two resonance structures of the reactive intermediate that accounts for the formation of 1,2- and 1,4-addition products upon reaction of 1,3-butadiene with one equivalent of bromine.

Question 75

A reaction in which two reactants add together in a single step to form a cyclic product is known as a _____.
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