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Solutions for Amines
H2O
NO2
N
C
N
H NO2
H
N
NO2H
N
C
N
H NO2
H
N
N
11 Nitration at the 4-position of pyridine is not observed for the same reason that nitration at the 2-
position is not observed: the intermediate puts some positive character on an electron-deficient nitrogen, 
and electronegative nitrogen hates that. (It is important to distinguish this type of positive nitrogen without a 
complete octet of electrons, from the quaternary nitrogen, also positively charged but with a full octet. It is 
the number of electrons around atoms that is most important; the charge itself is less important.)
GOOD: VERY BAD:
mechanism
VERY BAD—
N does not have
an octet of electrons.
not 
produced 
because of
unfavorable 
intermediate
N
O
O
C
N
SO3
H
H
H
HSO4
–
N
SO3
H
H
SO3
C
NH
H
H2SO4
C
N
SO3
H
H
H
SO3H
N
H
O
S
O
O
N
H
12 Any electrophilic attack, including sulfonation, is preferred at the 3-position of pyridine because the 
intermediate is more stable than the intermediate from attack at either the 2-position or the 4-position. 
(Resonance forms of the sulfonate group are not shown, but remember that they are important!)
The N of pyridine is basic, and in the strong acid mixture, it will be protonated as shown here. That is part 
of the reason that pyridine is so sluggish to react: the ring already has a positive charge, so attack of an 
electrophile is slowed.
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