AMINES
605
22.4
The electrondonating amino group and the electronwithdrawing nitro group are directly conjugated
in
p
nitroaniline. The planar geometry of
p
nitroaniline suggests that the delocalized resonance form
shown is a major contributor to the structure of the compound.
22.5
The p
K
b
of an amine is related to the equilibrium constant
K
b
by
p
K
b
log
K
b
The p
K
b
of quinine is therefore
p
K
b
log (1
10
6
)
6
the values of
K
b
and p
K
b
for an amine and
K
a
and p
K
a
of its conjugate acid are given by
K
a
K
b
1
10
14
and
p
K
a
p
K
b
14
The values of
K
a
and p
K
a
for the conjugate acid of quinine are therefore
K
a
1
10
8
and
p
K
a
14
p
K
b
14
6
8
22.6
The Henderson
–
Hasselbalch equation described in Section 19.4 can be applied to bases such as
amines, as well as carboxylic acids. The ratio [CH
3
NH
3
] [CH
3
NH
2
] is given by
The ionization constant of methylammonium ion is given in the text as 2
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 Fall '01
 Reynolds
 Organic chemistry, Electron, pH, Amine, Amide, quinine, pKb

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