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176 CHAPTER 6 
 
4a
N
O
N
O
HH
H
4b
N
O
N
O
HH
H
4c
N
O
N
O
HH
H
 
 
If we inspect resonance structure 4c, we see why the highlighted carbon atom is electrophilic. In fact, when we draw 
this resonance structure, we can see the nucleophilic attack more clearly: 
 
 
 
(c) The new chiral center is highlighted below. The oxygen atom takes priority #1, while the H has priority #4. 
Between #2 and #3, it is difficult to choose because both are carbon atoms and each of them is connected to C, C, and 
H. The tie breaker comes when we move farther out, and one of the carbon atoms is connected to O and N, while the 
other is connected to N. The former wins, giving the R configuration: 
 
 
 
The newly formed chiral center has the R configuration, and not S, because the pendant nucleophile is attacking from 
above, so the O must end up on a wedge: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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