271
+ H 3 N
O –
O
+ H 3 N
OH
O
OH
+ H 3 N
O –
O
O
OH
+ H 3 N
OH
O
O
OH
+ H 3 N
OH
O
OH
O
+ H 3 N
O –
O
OH
O
H 2 N
O –
O
+ H 3 N
+ H 3 N
OH
O
HN
+ H 2 N
NH 2
H 2 N
O –
O
HN
HN
NH 2
-341.0
-342
-340.5
(pH 1.5)
-325.0
-249.8
-324.7
-329.0
-348.9
(pH 11.5)
-338.9
-338
-339.2
-346.8
-296.6
-296.5
-308.6
-342.0
H 2 N
O –
O
HN
+ H 2 N
NH 2
-341.0
(pH 7)
-296.0
-310.0
-310.6
-340.5
-340.3
N
H 2
+
O –
O
N
H 2
+
OH
O
N
H 2
+
HO
O
O –
N
H
NH 3
+
O
O
6.1 15 N NMR Spectroscopy