For example, aminoethanoic acid
(the amino acid glycine) has the formula H 2 N.CH 2 .COOH. However,
under neutral conditions, it exists in
the different form of the zwitterion
+ H 3 N.CH 2 .COO
– , which can be regarded as having been produced by
an internal neutralization reaction
(transfer of a proton from the carboxyl group to the amino group).
Aminoethanoic acid, as a consequence, has some properties characteristic of ionic compounds; e.g. a
high melting point and solubility in
water. In acid solutions, the positive
ion
+ H 3 NCH 2 COOH is formed. In
basic solutions, the negative ion
H 2 NCH 2 COO
– predominates. The
name comes from the German zwei,
two.
565
zwitterion
z
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