Deck 20: Dienes, Conjugated Systems, and Pericyclic Reactions

Question 1

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

Answer 1

3

Question 2

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

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

Answer 2

2

Question 3

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

Answer 3

(3S,4E)-3-ethyl-3,4-dimethyl-1,4-hexadiene

Question 4

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 5

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 6

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 7

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 8

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 9

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 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

Which of the following are conjugated dienes?

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

Question 12

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 13

Which of the following are conjugated dienes?

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

Question 14

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

Question 15

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

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

Question 16

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

Question 17

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 18

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 19

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 20

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

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

Question 21

The conjugated portion of the following molecule is circled.

Question 22

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

A)"n $\rarr$ $\pi$ *"
B)" $\pi$ $\rarr$ $\pi$ *"
C)" $\sigma$$\rarr$ $\pi$ *"
D)" $\sigma$ $\rarr$ $\pi$ "

Question 23

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 24

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 25

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

A)"A = log (I_o/I)"
B)"A = $\varepsilon$ cl"
C)" $\Delta$ E = hv"
D)"A = $\lambda$ _maxl"

Question 26

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 27

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

Question 28

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 29

What are the units of $\varepsilon$ in ultraviolet-visible spectroscopy?

A)M^-1.cm^-1
B)M.cm
C)J.mol^-1.M^-1
D)none, $\varepsilon$ is a dimensionless quantity

Question 30

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 31

Which of the following electronic transitions is (are) apparent in the ultraviolet-visible spectrum of acrolein, H₂C=CHCHO?
1)n $\rarr$ $\pi$ *
2) $\pi$ $\rarr$ $\pi$ *
3) $\sigma$$\rarr$ $\pi$ *

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

Question 32

The conjugated portion of the following molecule is circled.

Question 33

Which of the following has the highest value of $\lambda$ _max in the ultraviolet-visible spectrum?

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

Question 34

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 35

What are the units of $\lambda$ _max in ultraviolet-visible spectroscopy?

A)J.mol^-1
B)M^-1
C)nm
D)none, $\lambda$ _max is a dimensionless quantity

Question 36

Which of the following has the highest value of $\lambda$ _max in the ultraviolet-visible spectrum?

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

Question 37

What quantity is abbreviated as $\varepsilon$ in ultraviolet-visible spectroscopy?

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

Question 38

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 $\mu$ m
D)2-10 mm

Question 39

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 40

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 41

What is the IUPAC name of the following compound?

Question 42

The following spectrum could arise from $\pi$ to $\pi$ * transitions.

Question 43

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 _____.

A)A
B)B
C)C
D)D

Question 44

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

Question 45

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 _____.

A)A
B)B
C)C
D)D

Question 46

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

Question 47

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

Question 48

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 _____.

A)A
B)B
C)C
D)D

Question 49

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

Question 50

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 ____.

A)A
B)B
C)C

Question 51

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

Question 52

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

-Based on the following table.
Compound
$\lambda$ _max (nm)
W
190
X
340
Y
560
Z
250
Compound ______ has the largest energy difference between the HOMO and LUMO.

Question 53

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 ____.

A)A
B)B
C)C

Question 54

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 55

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

Question 56

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 ____.

A)A
B)B
C)C
D)D

Question 57

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 58

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

Question 59

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

-Consider the following spectrum for a conjugated diene. If a similar spectrum were taken for a conjugated tetraene, the $\lambda$ _max would be _________than 217 nm.

Question 60

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 ____.

A)A
B)B
C)C
D)D

Question 61

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

Question 62

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

Question 63

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

Question 64

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 65

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

Question 66

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 67

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 68

What is the IUPAC name of the following compound?

Question 69

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