chapter 18 hw: e.a.s. reactionspage 7 e.a.s. reactions 12. gives the reagents necessary to complete...
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CHAPTER 18 HW: E.A.S. REACTIONS
MECHANISM OF HALOGENATION, NITRATION AND SULFONATION
1. Give the complete curved arrow mechanism for each reaction, including the generation of the electrophile.
2. Use your mechanism for question 1a to briefly explain why FeCl3 is a catalyst for the halogenation reaction.
Cl2, FeCl3a.Cl
b. HNO3, H2SO4NO2
c. SO3, H2SO4SO3H
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3. Which energy diagram represents this reaction?
MECHANISMS OF FRIEDEL CRAFTS ALKYLATION + ACYLATION
4. Give the curved arrow mechanism for each Friedel Crafts reaction.
NO2+NO2
+ H++
CH3CH2Cla.
AlCl3
b.AlCl3
Br
c.Cl
AlCl3
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5. Give the curved arrow mechanism for each E.A.S. reaction.
6. Give the complete curved arrow mechanism for each Friedel Crafts reaction.
a.H2SO4
b. OHH2SO4
a. Cl
O
AlCl3
O
b.
O
O
Cl
OCl
O
AlCl3
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RATES OF E.A.S. REACTIONS
7. Would each compound react faster or slower than benzene in a halogenation reaction?
Faster or
Slower?
8. Rank each set in order of increasing rate of reaction towards Cl2 and FeCl3. (Hint: how do the
substituents affect the energy of the intermediate?) Explain the trend in detail.
OCH2CH3N
CH3CH3
CH3
Br NH2 O
O
a.
O
b.OCH3 CF3
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ORTHO-PARA AND META DIRECTORS
9. Reaction of phenol with Cl2 / FeCl3 can theoretically form three products: from ortho, meta and para addition. a. Draw resonance structures of the intermediate that leads to each product.
Reaction Resonance Structures of the Intermediate
b. Use the intermediate structures to explain why the product ratios are as follows:
Phenol + Cl2, FeCl3 à p-chlorophenol (86.6%) + o-chlorophenol (11.4%) + meta (0%)
Cl2OHOH
FeCl3 Cl
Cl2OHOH
FeCl3
Cl
Cl2OHOH
FeCl3 Cl
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10. Use resonance structures to rationalize the product distribution for this reaction.
Toluene + PhCOCl, AlCl3 à para (89.2%) + meta (1.5%) + ortho (9.3%)
11. Use resonance structures to explain why nitration of acetophenone (PhCOCH3) adds the nitro group meta to the carbonyl instead of ortho or para.
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E.A.S. REACTIONS
12. Gives the reagents necessary to complete each reaction.
13. Give the major organic product for each reaction, showing only the monosubstitution product.
a. c.OCH3 OCH3
O
b. d.Br Br
Br Cl
HNO3a.H2SO4
g.CF3
HO
O2N
NO2
SO3H2SO4
b.AlCl3
h.
AlCl3
Cl
O
OCl
Cl
O
c.FeCl3
i.OCH3
OCl2
Cl
NH3 HNO3H2SO4
d.HNO3H2SO4
O
F3C
SO3H2SO4
j.
e. k.H2SO4
O
Cl
O
Ph
AlCl3
f. l.N Br2
O
FeCl3
Cl2
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14. In each reactant below there are two aromatic rings, yet one ring preferentially undergoes substitution. Briefly explain why one ring is more reactive than the other, then give the expected major product from monosubstitution.
ACTIVATORS AND OVERSUBSTITUTION
15. Phenols and anilines are so strongly activating that they sometimes don’t need catalysts in order to undergo substitution reactions, and they often over-substitute. Explain why a hydroxyl group is such a strong activator, while a methyl group is a weak activator. Use resonance structures with your explanation.
a.AlCl3
O
OCl
b.H2SO4
OH
OH CH3Br2, 0 oC
(no catalyst needed)
Br2FeBr3
CH3
Br
OH
Br
BrBr
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16. Explain why multiple-alkylation is common under the conditions of reaction (1), but does not occur in reaction (2).
ASSIGNMENT OF AROMATIC SIGNALS IN 1H NMR SPECTRA
17. Assign the peaks in each 1H NMR spectrum to hydrogen atoms in each structure. Then use resonance structures to help explain your assignment for the aromatic hydrogen atoms (why are certain H more shielded than others)?
Cl
O
CH3AlCl3
CH3
O
AlCl3
CH3ClCH3 CH3
+
CH3
(1)
(2)
a.
O
H
O
H
OH
b.
Cl(phenol H not
shown in NMR)
a
b
c
d
a
b
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E.A.S. REACTIONS LIMITATIONS
18. Explain in detail the following observations: a. No E.A.S. reaction occurs in the conditions below.
b. The meta product is formed in this reaction, even though the –NH2 is an ortho-para director.
REACTIONS OF SYNTHETIC UTILITY
19. Gives the reagents necessary to complete each reaction.
NAlCl3
CH3Clno E.A.S. reaction
NH2 NH2
NO2
HNO3H2SO4
(followed by NaHCO3 neutralization)
a. c.
OS
OH
O O
b. d.NO2 NH2
O
Cl
(2 steps)
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SYNTHESIS PROBLEMS
20. For each problem, choose which sequence of reagents would effectively perform the desired synthesis. Then explain why the other sequence is not as efficient or wouldn’t work.
Route 1: a) Cl2, FeCl3 b) HNO3, H2SO4
Route 2: a) HNO3, H2SO4 b) Cl2, FeCl3
Route 1: a) Br2, FeBr3 b) CH3CH2CH2Br, AlCl3
Route 2: a) CH3CH2COCl, AlCl3 b) Zn, HCl c) Br2, FeBr3
a.
Cl
NO2
b.
Br
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21. Starting with benzene or toluene, design a synthesis for each compound, showing all reagents and intermediates. Assume monosubstitution for each E.A.S. reaction. Some syntheses may require reactions other than E.A.S. reactions.
Target Compound Synthesis
(Begin with phenol)
Br
NO2
NO2
Br
O2N
HO3S
O
NH2
Cl
OCH3
NH2
NH2
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SUMMARY OF CH. 16-18 REACTIONS
22. Give the major organic product for each reaction, assuming conditions that encourage reaction of only 1 equivalent in all cases where multiple could occur.
HIa.
50 oC
b.180 oC
NCCN
c. CH3OHCl
Cl
Cld.
AlCl3
O
e.
H2N
CH3
Br2
f.H2SO4
O
CF3 HNO3