Deck 14: Conjugated Compounds and Ultraviolet Spectroscopy

Question 1

Name:

Answer 1

2,3,4,5-tetramethyl-2,4-hexadiene

Question 2

Exhibit 14-2
Consider the reaction below to answer the following question(s):
Refer to Exhibit 14-2.This reaction shows the preferred electrophilic addition of HBr to this unsymmetrical alkene.Draw the products of electrophilic addition to the opposite end of the conjugated diene.

Answer 2

Question 3

Exhibit 14-2
Consider the reaction below to answer the following question(s):
Refer to Exhibit 14-2.The product that results from 1,4-addition is _____.

Answer 3

C

Question 4

Name:

Question 5

When an organic molecule is irradiated with ultraviolet radiation,the energy absorbed by the molecule corresponds to:

A)the amount necessary to increase molecular motions in functional groups
B)the amount necessary to excite electrons from one molecular orbital to another
C)the amount necessary to "flip" the spin of atomic nuclei
D)the amount necessary to strip a molecule of one electron to generate a radical cation

Question 6

Exhibit 14-2
Consider the reaction below to answer the following question(s):
Refer to Exhibit 14-2.The electrophile in this reaction is ____.

Question 7

For a diene to undergo a Diels-Alder reaction it must:

A)be substituted with electron-withdrawing groups
B)be able to adopt an s-trans conformation
C)be substituted with electron-donating groups
D)be able to adopt an s-cis conformation

Question 8

Draw: 2-methyl-1,3-butadiene

Question 9

The amount of energy in electromagnetic radiation is related to the frequency and wavelength of the radiation.High energy radiation like gamma rays is of:

A)low frequency and short wavelength
B)low frequency and long wavelength
C)high frequency and short wavelength
D)high frequency and long wavelength

Question 10

2-Chloro-1,3-butadiene is polymerized to yield an excellent,expensive synthetic rubber with good weather resistance called:

A)diprene
B)isoprene
C)styrene
D)neoprene

Question 11

Which of the following compounds will react as a diene in a Diels-Alder reaction?

A)
B)
C)
D)

Question 12

Exhibit 14-2
Consider the reaction below to answer the following question(s):
Refer to Exhibit 14-2.The nucleophile in this reaction is ____.

Question 13

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

A)1,2-control
B)kinetic control
C)1,4-control
D)thermodynamic control

Question 14

Exhibit 14-2
Consider the reaction below to answer the following question(s):
Refer to Exhibit 14-2.The kinetically controlled product in this reaction is _____.

Question 15

Draw: (2Z,4Z)-hexadiene

Question 16

Which of the following compounds would show the longest wavelength λ_max in its UV spectrum?

A)
B)
C)
D)

Question 17

In 1839,Charles Goodyear discovered a process by which both natural and synthetic rubbers are hardened.This process is called:

A)diazotization
B)vulcanization
C)polymerization
D)condensation

Question 18

A physical constant that is the quantitative measure of the amount of UV light absorbed by a compound.

A)A
B)ε
C)λ_max
D)π^*

Question 19

For Diels-Alder cycloaddition reactions to take place most rapidly and in highest yield the dienophile must:

A)be substituted with electron-withdrawing groups
B)be able to adopt an s-trans conformation
C)be substituted with electron-donating groups
D)be able to adopt an s-cis conformation

Question 20

Exhibit 14-2
Consider the reaction below to answer the following question(s):
Refer to Exhibit 14-2.Write a stepwise mechanism that accounts for both of the products shown.Show all intermediate structures and electron flow with arrows.

Question 21

If ΔH°_hydrog for a monosubstituted alkene is 126 kJ/mol,which of the following systems is most likely to be a conjugated system?

A)3 double bonds,ΔH°_hydrog = 379 kJ/mol
B)2 double bond,ΔH°_hydrog = 254 kJ/mol
C)4 double bonds,ΔH°_hydrog = 505 kJ/mol
D)None of these are likely to be conjugated.

Question 22

​What would be the stereochemistry of the product of the following reaction? ​

Question 23

Based on the following table,in which compound is the energy difference between the HOMO and LUMO the largest? Compound
Λ_max (nm)
W
190
X
340
Y
560
Z
250

A)W
B)X
C)Y
D)Z

Question 24

Draw the skeletal formulas for the product of the reaction of the following with HBr.

Question 25

Consider the following data for a series of hypothetical plant pigments. Pigment
Ε
QT7
15,300
XR4
41,000
B78
30,800
L99
10,600
The Absorbance of a solution containing one of these pigments,measured in a 1.00 cm cell,was 0.345.Which pigment was in the solution?

A)QT7
B)XR4
C)B78
D)L99

Question 26

Based on the following spectrum,what is the energy in kilojoules per mole of photons that corresponds to the λ_max?

A)
B)
C)
D)
E)

Question 27

​Draw the mechanism of the Diels-Alder reaction between propenal and 2-methyl-1,3-butadiene.

Question 28

Exhibit 14-7
Consider the reaction below to answer the following question(s).
Refer to Exhibit 14-7.This is an example of a(n) ____________ reaction.

A)Woodward-Hoffman
B)conjugate addition
C)Diels-Alder
D)electrophilic addition

Question 29

What is the concentration of a solution of a plant pigment (ε = 37,500) if an Absorbance of 0.751 were obtained in a cell with a 5.00 cm path length?

A)
B)
C)
D)

Question 30

Which of the following arises from π to π* transitions?

A)
B)
C)
D)
E)

Question 31

​Draw the mechanism of the bromination of 2-ethyl-1,3-pentadiene.

Question 32

​The unit for molar absorptivity is:

A)​L/cm
B)​(L .mol)/cm
C)​L/(mol .cm)
D)​mol/L

Question 33

​Calculate the concentration of β-carotene in a sample which is placed in a cell with a pathlength of 1.0 cm and the UV absorbance reads 0.56.The molar absorbtivity of β-carotene is found to be 138,000 L mol^-1 cm^-1.

Question 34

​Which of the following compounds is the most stable?

A)​penta-2,3-diene
B)​2,4-hexadiene
C)​1,4-pentadiene
D)​3,6-octadiene

Question 35

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

A)close to 217 nm
B)less than 217 nm
C)greater than 217 nm

Question 36

​Draw the mechanism of the bromination of 1,3-pentadiene and indicate the major and minor products.

Question 37

Which of the following has the highest degree of conjugation? Atoms other than carbon and hydrogen are labeled.

A)
B)
C)
D)

Question 38

Exhibit 14-7
Consider the reaction below to answer the following question(s).
Refer to Exhibit 14-7.The diene in the reaction is ____.

Question 39

​Which of the following is the most likely to happen when a conjugated diene is irradiated with ultraviolet light?

A)​The bonds between different atoms in the molecule undergo symmetric stretching.
B)​A electron is promoted from the highest occupied molecular orbital to the lowest unoccupied molecular orbital.
C)​A electron is demoted from the lowest occupied molecular orbital to the highest unoccupied molecular orbital.
D)​The bonds between different atoms in the molecule undergo asymmetric stretching.

Question 40

Exhibit 14-7
Consider the reaction below to answer the following question(s).
Refer to Exhibit 14-7.The dienophile in the reaction is ____.