CHEMISTRY 212
EXAM 2
Thursday, February 10, 2011
Answer Key
Answer all 17 questions (150 pts).
1. (16) State whether each of the following molecules is aromatic or non-aromatic (the latter includes
anti-aromatic). In addition, give only the following data which enabled you to arrive at your conclusion:
fully cyclically conjugated – yes or no; # pi electrons involved in any conjugation.
H
N
a)
N
N
b)
N
N
c)
d)
N
N
non-aromatic; not
aromatic; cyclically
non-aromatic; not
aromatic; cyclically
cyclically conjugated;
conjugated; 6 pi
cyclically conjugated; conjugated; 2 pi
6 pi electrons
6 pi electrons
2. (12) State whether each of the following molecules is activated or deactivated compared to benzene. It is
not necessary to explain why.
a)
Br
b)
O
c)
N
H
Cl
deactivated
deactivated
d)
H
N
CO2H
O
activated
deactivated
3. (12) State whether further electrophilic substitution of each of the following molecules would occur in the
ortho / para or meta positions. It is not necessary to explain why.
a)
b)
O
c)
d)
SO3H
C N
meta
ortho / para
ortho / para
meta
4. (4) Circle, which of the following compounds would react most slowly with HNO3/H2SO4.
CO2H
Cl
OCH3
CH3
first one
5. (4) Circle, which of the following compounds would react most rapidly with HNO3/H2SO4.
CH3
Br
SO3H
NH2
fourth one
6. (4) Circle the major product of the reaction shown.
second one
7. (4) Which of the following sequences is the best synthesis of the compound shown below from
benzene? Answer D
8. (4) Which of the following is the best method of preparing p-nitrobenzoic acid from benzene?
Answer B
9. (26) Provide the reagents required to effect each of the following transformations.
O
1) NaBH4
2)
OH
H+
CHPh
PBr3
(or HBr)
OH
CH
Ph
H2SO4
Br
1) Mg 2) H2CO
CH2OH
3) H+
PCC
O
1) PhMgBr
C
2) H+
H
10. (6) Classify the following reagents as oxidizing or reducing.
a) LiAlH4
reducing
b)
CrO3 / H2SO4
oxidizing
c) H2 / Pd
reducing
11. (10) For the compound shown below, show all the resonance forms that illustrate the effect of the
group attached to the ring. In this case, you should show arrow-pushing to support your answer.
O
N
O
O
N
O
O
N
O
O
N
O
12. (14) Draw out a synthetic sequence for the preparation of each of the following molecules, starting
from the aromatic compound shown and using any other necessary reagents.
a)
COOH
NO2
HNO3 / H2SO4
KMnO4
H2O, heat
para +
O2N
b)
CH2Br
Br
CH3Cl
AlCl3
CH3
NBS, light
Br2
FeBr3
CH3
+ ortho
Br
13. (12) For each of the following compounds, indicate with an arrow the most likely ring carbon to be
nitrated on treatment with HNO3 / H2SO4.
a)
c)
b)
COCH3
d)
Cl
O
SO3H
CH3
CN
Cl
14. (4) Circle any intermediate shown below which would not arise from reaction of chlorobenzene with
SO3 / H2SO4.
Cl
Cl
Cl
Cl
SO3H
H
SO3H
SO3H
H
SO3H
15. (10) Name the following molecules using IUPAC rules.
F
HO
NO2
4-fluoro-3-nitrophenol
OH
4,5-dimethyl-2-hexanol
16. (4) State two potential problems with Friedel-Craft’s alkylation reactions.
1. Rearrangements of the intermediate carbocation can occur – leading to incorrect products.
2. Overalkylation (polyalkylation) is likely since the alkyl group added initially to the aromatic ring
activates the latter to further reaction.
3. Like the Friedel-Craft’s acylation reactions, alkylation will not occur on an aromatic ring
containing a strongly electron-withdrawing group.
17. (4) Indicate which of the following reactions are not possible. There could be more than 1 answer.
a. Benzene + bromine in the presence of FeBr3
b. Nitrobenzene + 1-chlorobutane, in the presence of AlCl3
c. PhCHO + CH3COCl, in the presence of AlCl3
d. Toluene + nitric/sulfuric acid mixture