pKas: Table of Data Group Acid Dissociation Reaction pKa

protonated nitro group

protonated nitrile

(nitrilium)

protonated ketone

protonated thiol

(sulfonium)

NO

OH N

O

O

H +

H +C N HCH3 C NCH3

H +CH3

CCH3

OH

CH3C

CH3

O

CH3 SH

HH + CH3 S

H

–11.3

–10.1

–7.2

–6.8

Strongest Acid Weakest Base

sp N+

sp2 O+

sp3 S+

Group Acid Dissociation Reaction pKa

protonated phenol

(oxonium)

protonated ester

protonated carboxylic

acid

protonated sulfide

(sulfonium)

H +CH3

COCH2CH3

OH

CH3C

OCH2CH3

O

CH3 SCH3

HH + CH3 S

CH3

OH

H

H +O

H

H +CH3

COH

OH

CH3C

OH

O

–6.7

–6.5

–6.1

–5.4

Why is carbonyl oxygen more basic? –6.2 (HCl) =

Group Acid Dissociation Reaction pKa

protonated ether

protonated amide

(amidinium)

carboxylic acid

(e– deficient)

phosphoric acid

H +CH3

CNH2

OH

CH3C

NH2

O

CH3CH2 OCH2CH3

HH +

H +CF3

CO

O

CF3C

O

O

CH3CH2 OCH2CH3

CH3CH2 OH

HH + CH3CH2 O

H

H

H +HO P OO

OH

HHO P O

O

OH

–3.6

–2.4

0.2

2.1

protonated alcohol

0

Group Acid Dissociation Reaction pKa

anilinium

pyridinium

iminium

imidazolium

H +CH3

CCH3

NH

H +CH3

CO

O

CH3C

O

OH

NH

HH

H + NH

H

H +NH

N

CH3

CH3C

CH3

NCH3

N

N

H

H

H +

N

NH

4.6

4.7

5.5

7.0

carboxylic acid

5.3

Group Acid Dissociation Reaction pKa

phosphoric acid

(monobasic)

1,3-diketone

ammonium

phenol O

H H + O

H +HO P OO

OH

HO P OO

O

H +

CCC

CH3

O

S

OCH3CH2

H HC

CCCH3

O

S

OCH3CH2

H

H +C

CCCH3

O

CH3

O

H HC

CCCH3

O

CH3

O

H

CH3 N HCH3

CH3

H + CH3 NCH3

CH3

7.2

8.5

9.8

10.0

β-keto thioester

9.0

Group Acid Dissociation Reaction pKa

thiol

iminium (C-H acid)

phosphate (dibasic)

guanidinium

H +O P OO

O

H +

CCC

CH3

O

O

OCH3CH2

H HC

CCCH3

O

O

OCH3CH2

H

H +

CH3CH2S

H H + CH3CH2S

CH3C

C

NCH3 CH3

H

HH

H +CH3

CC

NCH3 CH3

H

H

HO P O

O

O

NC

N

NH H

H

HH

CH3 NC

N

NH

H

HH

CH3

10.5

11.0

12.4

13.2

β-keto-ester

11.0

Group Acid Dissociation Reaction pKa

imidazole

alcohol

ketone

ester

CH3CH2O

H H + CH3CH2O

CH3C

N

OH

H

H +

H +N

NH

N

N

CH3C

N

O

H

CH3C

C

OH

H

H +CH3

CC

O

HH

H

OCH2CH3C

C

OH

H

H +OCH2CH3

CC

O

HH

H

14.4

15.0

20

24.5

amide

15.9

Group Acid Dissociation Reaction pKa

terminal alkyne

amine

benzylic C-H

H +

H +

H +

H +

C C HH C CH

C NCH

HH

C NCH

H

CH3 NH

HCH3 N

H

CH

HH C

H

H

25

25

41

nitrile (α C-H)

35

Group Acid Dissociation Reaction pKa

benzene

alkane hydrogen H +

H +

H +

HCH

CH3H

HH

H

HH

H

HH

HH

H

C CH

HH

HC C

HH

H

HCCH3

H

43

44 vinyl hydrogen

50

Weakest Acid Strongest Base