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524 Chapter 16
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b.
fraction present in the acidic form
=
3
H
+
4
K
a
+
3
H
+
4
3
H
+
4
K
a
+
3
H
+
4
=
3.2
*
10
-
2
3.2
*
10
7
+
3.2
*
10
-
2
=
3.2
*
10
-
2
3.2
*
10
7
=
1
*
10
-
9
c.
fraction present in the basic form
=
K
a
K
a
+
3
H
+
4
K
a
K
a
+
3
H
+
4
=
1.0
*
10
-
6
1.0
*
10
-
6
+
3.2
*
10
-
2
=
1.0
*
10
-
6
3.2
*
10
-
2
=
3.1
*
10
-
3
31.
a.
C N
NH
2
H
b.
C N
CH
3
CH
2
OH
32.
a.
Notice that both of these mechanisms have a feature that we have seen in many mechanisms—formation of three tetrahedral intermediates: a protonated tetrahedral intermediate, then a neutral tetra-
hedral intermediate, and then a second protonated tetrahedral intermediate.
1.
+
N
R
H B
+
N
R
H
+
+
H
2
O
NHR
OH
+
H B
NHR
OH
H B
+
NH
2
R
OH
+
B
OH
+
RNH
2
+
O
+
RNH
3
+
protonated
tetrahedral
intermediate
neutral tetrahedral
intermediate
protonated tetrahedral
intermediate