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658 CHAPTER 18 
 
not have been achieved via direct alkylation (due to the 
problem of carbocation rearrangements). Then, a nitro 
group is installed in the para position because of the 
directing effects (and steric effects) of the propyl group. 
Bromination then installs the bromine atom in the correct 
location (ortho to the activating group), and finally, 
reduction of the nitro group gives the product. 
 
H2N Br
1) CH3CH2COCl,
AlCl3
2) HCl, Zn(Hg),
heat
3) HNO3, H2SO4
4) Br2, AlBr3
1) CH3CH2COCl,
AlCl3
2) HCl, Zn(Hg),
heat
HNO3,
H2SO4
O2N Br2,
AlBr3
O2N Br
5) Zn, HCl
1) Zn, HCl
6) NaOH
2) NaOH
 
 
The strategy above represents just one method for 
making the desired the compound. There are often other 
acceptable solutions. For example, the nitro group and 
the bromo group can be installed in the opposite order 
(first the bromo group and then the nitro group), 
although this would require a blocking group (to help 
direct the incoming bromo group into the ortho position). 
The first method (shown above) avoids the need for a 
blocking group. 
 
 
 
 
 
(c) While there is more than one way to achieve the 
desired transformation, the following strategy is perhaps 
the most efficient, as it avoids the need for a blocking 
group. The tert-butyl group is first installed, and its 
directing effects are exploited to install an amino group 
in the para position (installation of the amino group 
requires a two-step process – nitration, followed by 
reduction). Finally, chlorination in the presence of 
excess Cl2 gives the desired product (AlCl3 is not used 
because the ring is highly activated). The regiochemical 
outcome of the final step is controlled by the electronic 
effects of the amino group (in concert with the steric 
effects of the tert-butyl group). 
 
 
 
(d) The following retrosynthetic analysis represents one 
strategy for preparing the desired compound. An 
explanation of each of the steps (a-c) follows. 
 
a
b
c
Br
SO3H
Cl
Br
Br
SO3H
 
 
a. The product can be prepared via chlorination of 
the disubstituted ring shown. 
b. The disubstituted ring can be prepared via 
sulfonation. 
c. The monosubstituted ring (bromobenzene) can be 
prepared from benzene. 
 
Now, let’s draw the forward scheme. First, a bromine 
atom is installed via bromination in the presence of a 
Lewis acid. Then, a sulfonic acid group is installed. 
During this sulfonation step, the bromine atom directs 
the incoming sulfonic acid group into the para position. 
And finally, chlorination will install the bromine atom in 
the correct location (ortho to the ortho-para directing 
bromine atom). 
 
 
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