CEM252 Quiz 4
1. a. Fill the boxes with reagents for the transformations 3 to 8. (6 pts)
b. In the space provided draw the cationic species that serves as the actual electrophile in the
following EAS reactions 1, 2, 4 and 5. (4 pts)
CEM252 Quiz 4
2. Predict the products for the following reaction and provide the structures in the boxes.
3. a. Which of the following reactions would produce isopropylbenzene as the major product?
(2 pts)
A. I
B. II
C. both I and II
Ans: C
b. Justify your choice in the space below. (2 pts)
1,2-hydride shift happens quick for the primary carbocation generated in reaction II
Benzene ring attacks the secondary carbocation and give the major product as
isopropylbenzene.
CEM252 Quiz 4
4. The carbocation shown below can take other resonance forms.
a. In the boxes provided show two of those resonance structures (including the pushing arrow).
(4 pts)
b. Describe in words the steps 1 to 3 of this electrophilic aromatic substitution (EAS) reaction.
(3 pts)
Ans: 1. Formation of an electrophile
2. The pi electron of the ring attacks an electrophile
3. Deprotonation of sigma complex to restore aromaticity
CEM252 Quiz 4
1. Cyclohexene undergoes an addition reaction with Br2, but benzene does not. Instead
benzene undergoes a substitution reaction with Br2. Explain why. (3 pts)
Ans: Cyclohexene has localized electrons, whereas benzene has delocalized electrons.
Addition of bromine to benzene would result in loss of aromatic stabilization, as the product
formed would be nonaromatic.
2. Which of the following substituents will not direct the incoming group to the
ortho/para position during electrophilic aromatic substitution? (2 pt)
A:
B:
C:
D:
E:
-CH2CH3
-CF3
-OCH3
-NHCH3
-Br
Ans B
3. Circle the compounds which has meta directing group. (5 pts)
CEM252 Quiz 4
4. The carbocation shown below can take other resonance forms.
a. In the boxes provided show two of those resonance structures (including the pushing arrow).
(4 pts)
b. Describe in words the steps 1 to 3 of this electrophilic aromatic substitution (EAS) reaction.
(3 pts)
Ans: 1. Formation of an electrophile
2. The pi electron of the ring attacks an electrophile
3. Deprotonation of sigma complex to restore aromaticity
CEM252 Quiz 4
5. Provide the reagents necessary to carry out the following conversion in 2 steps. (4 pts)
1.
2. Zn(Hg), HCl, heat
6. Provide the structures in the boxes. (4 pts)