Chemistry 218, Problem Set 6
Recommended problems from the text: 17.3-17.4, 17.10, 17.12-17.16, 17.18-17.22,
17.25-17.31, 17.33-17.42, 17.44-17.45, 17.53, 18.1-18.24, 18.32 (a-g), 18.33-18.37,
18.40-18.48, 18.51, 18.54 (a-e), 18.64-18.65
(Recommended problems from the text, 1st ed.: 17.3-17.4, 17.9, 17.11-17.15, 17.1717.21, 17.24-17.31, 17.33-17.44, 17.50, 18.1-18.25,18.34 (a-g), 18.35-18.39, 18.4218.51, 18.54, 18.57 (a-e), 18.66-18.67)
1. Draw mechanisms for each product formed in the following transformations. Include
ALL resonance structures of carbocation intermediates.
NH2
NH2
NH2
NO2
HNO3
+
H2SO4
NO2
O
O
N
OH
HO
O
O
O
S
O
O
N
OH2
O
S
OH
O
B
NH2
NH2
O
O
OH
H
N
O
B
NH2
NO2
H
B
NH2
NO2
N
H
B
NH2
NO2
H
NO2
O
NH2
NO2
NH2
NH2
NH2
NH2
NH2
NH2
NO2
NO2
NO2
NO2
NO2
O
N
O
NH2
-H+
NO2
(b)
O
O
Br2, FeBr3
Br
Br
FeBr3
Br
O
Br
Br FeBr3
O
Br
O
O
Br FeBr3
H
Br
Br
B
O
Br
2. Choose the most stable carbocation from each of the following pairs.
(a)
Br
NH2
NH2
R
R
NH2
NH2
NH2
R
R
R
3 resonance
structures
NH2
NH2
NH2
R
NH2
R
R
R
4 resonance
structures, pos. charge
distrib. onto N, more stable
carbocation
(b)
O
R
O
R
R
R
O
R
O
R
R
R
O
O
R
R
R
O
R
R
R
R
O
O
R
O
R
R
R
R
this resonance structure is
destabilized by the EWG, which is
pulling electrons away from a carbon
which is already positively charged.
Therefore, this carbocation is the least stable.
3.
(a) If benzene is treated with with sulfuric acid for several days at room
temperature in the presence of D2O, the following reaction occurs:
D
H+
+
D2O
+
HOD
Draw a mechanism to explain the reaction. (Hint: what happens first when you
put acid into water?)
First, an acid/base reaction occurs:
H2SO4
+
HDSO4
D2SO4
D2O
+
+
HOD +
D 2O
Benzene is then protonated by sulfuric acid. It is likely that some if not all will
be protonated with deuterium.
two others
D
D+
H
-H+
D
4.
Predict whether single or multiple substitution is expected for the following
reactions with benzene, if the reagents are used in a large excess, Explain WHY.
(a) Nitration Only mono substitutions will occur because nitro groups are
strongly deactivting groups. After one nitro group is introduced, the ring is
deactivated toward further substitution.
(b) Sulfonation SO3H groups are moderately deactivating, so it is unlikely that a
second substitution would occur.
(c) Friedel-Crafts alkylation Alkyl groups are activating groups, so further
alkylations will occur. The more alkyl groups that are installed, the more
activated the ring will be.
(d) Friedel-Crafts acylation Acyl groups are moderately deactivating groups, so
it is unlikely that further acylations will occur.
(e) bromination Bromines are weakly deactivating, so a second bromination is
possible, though it will be much more difficult that the first.
5. Draw a reaction coordinate for an EAS reaction with a halobenzene compared to
benzene.
benzene
halobenzene
E
r.c
6. Each interesection of the following table represents a reaction. What products (if any)
are formed in each reaction? Which reactions occur more rapidly than the analogous
reaction on benzene itself? Assume only mono substitutions occur.
reacts faster
than benzene
reacts faster
than benzene
O
Br
Br
O
Br2, FeBr3
Br
Br
HNO3, H2SO4
Br
O
O
Br
Br
O
NHCOMe
NH2
Me
NO2
NHCOMe
NHCOMe
Me
Me
Br
O
NHCOMe
NO2
Me
O
Br
NO2
NH2
NO2
Me
Me
AlCl3,
NH2
NO2
NO2
Me
Me
NHCOMe
Br
NO2
NO2
NHCOMe
Br
NH2
Br
NO2
NH2
Br
Br
NO2
NO2
NH
NH2
NO2
Br
NO2
NH2
Br
Br
Br
AlCl3, MeCl
NO2
reacts faster
than benzene
O
O
Br
NH2
NHCOMe
O
NHCOMe
NH2
NO2
Cl
Me
Me
O
O
O
O
O
O
O