Chapter3-pKa table

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SO3 / FSO3H/SbF5
HF / SbF5
F3CSO3H
SbF6–
SbF6–
F3CSO3–
Super Acids
all too strong to measure
R C
H
O
H
+ R C
H
O
R C
OR'
O
H
+ R
C
OR'
O
R C
R'
O
H
+ R
C
R'
O
–6
X O
H
H
+ –6
X
N
H
H
H
+
X
N H
H –6 to +5
protonated aldehydes
protonated esters
protonated carboxylic acids
protonated ketones
protonated phenols
second H of sulfuric acid
nitrous acid
–??
–10
–10
–8
–7
–7
–7
HCl
HClO4
HI
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Acid Conj. Base pKa Comment
ClO4–
Cl–
I–
SO42–
F–
NO2–
1.99
3.18
3.3HNO2
H–F
HSO4–
anilines; pKa very sensitive 
to ring substituents
hydrochloric acid
hydrofluoric acid
–9HBr Br–
–9H2SO4 HSO4– sulfuric acid
hydrobromic acid
R C
OH
O
H
+ R
C
OH
O
H3C
S
O
O
OH
aka TsOH
H3C
S
O
O
O
–3 sulfonic acids
X O
H
R
O
R'
H
+
R
O
R'
–3
R
O
H
H
+
R
O
H
–2
protonated ethers
protonated alcohols
hydronium; H+(aq)
nitric acid
H2OH3O+ –1.74
NO3– –1.3HNO3
R C
O
O-H R C
O
O
H3C
C
O
C
C
O
CH3
H H
H3C
C
O
C
C
O
CH3
H
X O
H
X O
H3C
C
O
C
C
O
OEt
H H
H3C
C
O
C
C
O
OEt
H
EtO
C
O
C
C
O
OEt
H H
EtO
C
O
C
C
O
OEt
H
H
H
H
R C
O
N
H
H
R C
O
N
4.0 to 5.0
H
R C
O
C
H2CO3 HCO3– 
H2S HS–
9.00
H
H
H
R C
O
C
4–11
H
H
10.0
10.3
RO C
O
C
H
H
H
RO C
O
C
13.0
H
H
15.0
11.0
R C C
17.0
H
20-21
25
R–CH2–CN
R C C
R–CH–CN 25
25
HCO3–
7.00
6.35
NH4+ NH3 9.24
15.7
16-19
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Acid Conj. Base pKa Comment
OH–
R–CH–NO2
R–O–H
H–O–H
R–CH2–NO2
CO3–
terminal alkynes.
The electrons are in an 
sp hybridized orbital
alpha to nitrile
R O
depends on substitution
plain phenol has a pka=10
aliphatic nitro
bicarbonate
ethyl acetoacetate
diethyl malonate
water pKa
ammonium ion
2,4-pentandione
hydrogen sulfide
carbonic acid
carboxylic acids
cyclopentadiene: World's
Strongest Carbon Acid!!
alpha H of ketones
alcohols, ethanol pKa = 16
amides
alpha H of esters
Acid Conj. Base pKa Comment
X
N
H
H
X
N
H
C
C
CH
H
H H
H
H
H
H
H H
H
C
CH
H
H
H CH
H
H
C H
HH
H
H H
HH
H
H H
H2C
H2C
C
H
H H2C
H2C
H
H
C
H H
H
H
C
H
H
H
H
HH
H
H H
H
H
H
H
H
18–28
H
HH
H
H H
H
H
H
H
H
44
46
43
48
44
52
H2 36
((CH3)2CH)2NH ((CH3)2CH)2N– 40
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H
C
C
C
C
C
C
anilines; pKa Depends on 
substitution. Low because it 
has a conjugated base.
Plain aniline has pKa =25
amines: NH3 pKa=38
cyclohexyl; weakest acid on 
this table. sp3 conj. base
methane and hydrogens on
sp3 carbons
cyclopropane H; more vinyl 
than sp3 hybrid (see below.)
vinyl hydrogens; electrons
in unconjugated sp2 orbital
phenyl hydrogens; electrons
in unconjugated sp2 orbital,
not part of aromatic π sextet
hydrogen gas is a weak acid
allyl hydrogens; conjugated
conjugate base.
updated 9/6/2016
C
H
HH
C H
H
41 benzyl hydrogens; 
conjugated base