Acidities of various compounds
Conjugate Acid
Conjugate Base
pKa
RNO2H+
RNO2
-12
RCNH+
RCN
-12
PH4+
PH3
-12
OH
Ar
C Cl
O
Ar
-11
C Cl
ArOH2+
ArOH
-7
ArNH3+
ArNH2
-10 to +5
RSH2+
RSH
-7
HI
I–
-8.5 to –9.5
HBr
Br–
-8 to –9
HCl
Cl–
-6 to –7
ArOR
-6 to –8
O
-3 to –5
Ar
OR
H
OH
ArCAr
OH
R C G
ArCAr
O
-2 to –8
R C G
(G = H, R, Ar, OR, OH)
R2OH+
R2O
-2 to –5
ROH2+
ROH
-2 to –5
H3O+
H2O
-1.74
OH
CH3SCH3
Acidities.doc
O
-1.5
CH3SCH3
page 1
OH
O
0 to –4
RCNH2
RCNH2
HF
F–
3.18
RCOOH
RCOO–
4 to 5
H2S
HS–
7.0
ArSH
ArS–
8
O
O
R C CH2
C
O
O
R
R C CH C
9
R
HCN
CN–
9.21
NH4+
NH3
9.25
ArOH
ArO–
9 to 11
RCH2NO2
RCHNO2–
10
RNH3+
RNH2
10 to 12
RSH
RS–
12
H2O
OH–
15.7
16
H
RO–
ROH
17 to 20
18
Ph
H
ArNH–
ArNH2
O
R C CH2
Acidities.doc
Ph
O
R
18 to ~28
19 to 20
R C CH R
page 2
20
H
PhC≡C–
PhC≡CH
23
23
H
HC≡CH
HC≡C–
24
O
O
24
RO C CH2
R
RO C CH R
PH2–
PH3
29
~30-35
H
Ph3CH
Ph3C–
31
CH3SO2CH3
CH3SO2CH2–
31
CH3CN
CH2CN–
31
NH3
NH2–
32.5
Ph2CH2
Ph2CH–
33
CH3SOCH3
CH3SOCH2–
35
H2
H–
35
PhCH3
PhCH2–
41
Cyclohexanamine
Cyclohexanamide
42
PhH
Ph–
43
CH2=CHCH3
CH2=CHCH2–
43
Acidities.doc
page 3
CH2=CH–
CH2=CH2
44
44
H
H
46
46
H
CH3–
CH4
Ph
Ph
H
Ph
~50
Ph
Ph
Ph
50
H
51
H
52
H
~55
H
(CH3)3CH
50
(CH3)3C–
~65
Source:
T.H. Lowry and K.S. Richardson, Mechanism and Theory in Organic Chemistry, 3rd Ed., New York:
Harper & Row (1987), pp. 294-298
Acidities.doc
page 4