This page has acidity tables for heteroatom organic acids and carbon acids.

Because of the very large range of acid strengths ( greater than 1040 ), a logarithmic scale of acidity ( pKa ) is normally employed. Stronger acids have smaller or more negative pKa values than do weaker acids. A discussion of acid-base terminology is available here. The pKa values given here are extrapolated for water at 25 ºC.

Other collections of pKa values include those compiled by Prof. D.A. Evans (Harvard); a large list compiled by W.P Jencks & F.H. Westheimer, presented by R. Williams (Penn. State); and a collection of pKa measurements in DMSO solution, compiled by Prof. F.G.Bordwell and presented by Prof. H.J.Reich (Wisconsin).

Ionization Constants of Heteroatom Organic Acids

Common Name

Formula

Acidity Constant

pKa

trifluoromethanesulfonic acid

CF3SO3H

ca. 1013

ca. -13

benzenesulfonic acid

C6H5SO3H

ca. 103

ca. -2.5

methanesulfonic acid

CH3SO3H

ca. 3 * 102

ca. -2.0

trifluoroacetic acid

CF3CO2H

1.0

0.0

picric acid

(O2N)3C6H2OH

0.5

0.3

squaric acid

K1 = 0.33
K2 = 3.3 * 10-4

1.5  
3.5  

trichloroacetic acid

CCl3CO2H

0.23

0.77

oxalic acid

(CO2H)2

K1 = 6.5 * 10-2
K2 = 6.1 * 10-5

1.2  
4.2  

dichloroacetic acid

CHCl2CO2H

5.5 * 10-2

1.25

fluoroacetic acid

FCH2CO2H

2.5 * 10-3

2.6

chloroacetic acid

ClCH2CO2H

1.36 * 10-3

2.87

citric acid

C(OH)(CH2CO2H)2CO2H

K1 = 7.4 * 10-4
K2 = 1.7 * 10-5
K3 = 4.0 * 10-7

3.13  
4.76  
6.40  

formic acid

HCO2H

1.77 * 10-4

3.75

ascorbic acid

K1 = 6.7 * 10-5
K2 = 2.5 * 10-12

4.17  
11.6  

benzoic acid

C6H5CO2H

6.3 * 10-5

4.20

acetic acid

CH3CO2H

1.77 * 10-5

4.75

thiophenol

C6H5SH

2.5 * 10-7

6.6

tropolone

2.0 * 10-7

6.7

p-nitrophenol

O2NC6H4OH

5.7 * 10-8

7.2

peracetic acid

CH3COO2H

5.7 * 10-9

8.2

succinimide

(CH2CO)2NH

2.5 * 10-10

9.6

phenol

C6H5OH

10-10

10.0

chloral hydrate

CCl3CH(OH)2

10-10

10.0

benzenesulfonamide

C6H5SO2NH2

8 * 10-11

10.1

2-hydroxy-2-cyclohexenone

5.0 * 10-11

10.3

ethanethiol

C2H5SH

2.5 * 10-11

10.6

acetoxime

(CH3)2C=NOH

6 * 10-13

12.2

2,2,2-trifluoroethanol

CF3CH2OH

4 * 10-13

12.4

imidazole

C3H3N2H

3.3 * 10-15

14.5

pyrrole

C4H4NH

10-15

15

ethanol

C2H5OH

10-16

16

1°-amides

RCONH2

10-17

17

p-nitroaniline

O2NC6H4NH2

3.3 * 10-19

18.5

t-butanol

(CH3)3COH

10-19

19

aniline

C6H5NH2

10-27

27

1,1,1,3,3,3,-hexamethyldisilazane

[(CH3)3Si]2NH

10-30

30

pyrrolidine

C4H8NH

10-32

32

diisopropylamine

[(CH3)2CH]2NH

1.9 * 10-36

35.7

tetramethylpiperidine

10-37

37
     

Organic Chemistry
Michigan State University


Ionization Constants of Carbon Acids

Common Name

Formula

Acidity Constant

pKa

tricyanomethane

CH(CN)3

105

-5

dinitromethane

CH2(NO2)2

2.5 * 10-4

3.6

5,5-dimethyl-1,3-cyclohexadione

1.6 * 10-5

4.8

malonaldehyde

CH2(CHO)2

10-5

5.0

Meldrum's acid

8 * 10-6

5.1

2,4-pentanedione

CH2(COCH3)2

1.26 * 10-9

8.9

hydrocyanic acid

HCN

6.3 * 10-10

9.2

nitromethane

CH3NO2

6.3 * 10-11

10.2

malononitrile

CH2(CN)2

10-11

11.0

ethyl acetoacetate

CH3COCH2CO2C2H5

10-11

11.0

bis(methylsulfonyl)methane

CH2(SO2CH3)2

2.0 * 10-13

12.7

diethyl malonate

CH2(CO2C2H5)2

3.2 * 10-14

13.5

cyclopentadiene

  

10-16

16.0

phenylacetylene

C6H5C≡H

10-19

19.0

indene

10-20

20

tris(phenylthio)methane

(C6H5S)3CH

10-23

23

methyl ketones

RCOCH3

10-25

25

methylsulfones

RSO2CH3

10-25

25

alkyl esters

RCH2CO2C2H5

10-25

25

nitriles

RCH2CN

10-25

25

acetylene

HC≡CH

10-25

25

methylsulfoxides

RSOCH3

10-30

30

1,3-dithiane

(CH2)3S2CH2

10-31

31

triphenylmethane

(C6H5)3CH

3.2 * 10-32

31.5

diphenylmethane

(C6H5)2CH2

3.2 * 10-34

33.5

toluene

C6H5CH3

10-40

40

benzene

C6H6

10-43

43

ethene

C2H4

10-44

44

cyclopropane

C3H6

10-46

46

ethane

C2H6

10-48

48
   

Organic Chemistry
Michigan State University