Typical Pka Values For Organic Acids And Other Important Reagents In Organic Chemistry

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Typical pK
values for organic acids and other important reagents in organic chemistry
a
O
O
O
O
O
O
EtO
OEt
OEt
13
H
H
9
11
H
H
HCN
H
Ph
P CH
3
2
9.3
CH
CH
OH
O
-3
3
2
H
SO
OH
35
2
4
16
H
-3
H
C
OEt
O
O
H
H
C CH
H
2
2
H
O
H
+
H
O
H
C CN
2
H
C
OH
44
3
2
C
NMe
H
CH
3
15.7
2
i-Pr
NH
3
4.76
9.9
-1.7
H
H
2
2
60
40
25
30
HCl
-7
-10
-5
0
5
10
15
20
25
30
35
40
45
50
55
60
pK
scale
a
H
O
HNO
NH
3
O
O
H H
R
C C
H
3
+
CH
NH
-1.4
3
3
35
24
10.6
-7.3
H
17
19
OH
2
H
H
-2.7
NH
4.6
CH
SH
3
10.3
5.1
Reactions will prefer to go from a strong acid to a weak acid. The equilibrium constant for an acid base reaction will be the difference between the
pK
values of the two acids. The pK
scale is logarithmic, so difference of 1 pK
unit is equal to an equilibrium ratio of 10:1, 2 units is 100:1, 3 units
a
a
a
is 1000:1 and so on.
K
5.8
ONa
+ H
O
K = 10
OH + NaOH
2
An acid must have a pK
value more than 3 units higher than the conjugate acid of a base to fully protonate it (>99.9%). Thus, phenol is 6 pK
a
a
units more acidic than water, so hydroxide can fully deprotonate it. Hydroxide could not fully deprotonate ethanol, however.
An acid or base should be within at least 10 pK
to give a sufficient equilibrium concentration of a more acidic or basic species for a reaction to
a
5.6
occur. For example, protonation of a ketone is disfavored by 1:10
, but is sufficient to catalyze reactions. Protonation of a ketone by an alcohol
23
is unreasonable, though (disfavored by 1:10
).

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