Organic Chemistry pKa Values & Cation/Anion Donor/Acceptor Activity

Memorize for ranking cations/anions on acidity/basicity.

High pKa Value = Strong/Weak ACID

Weak ACID

High pKa Value = Strong/Weak BASE

Weak BASE

Cation

Positive Formal Charge

Electron Acceptor

H+ (proton) Donor

Electrophile

Usually an Acid —> Remove H to make CB

Weak CB (low pKa value) = Strong Acid

Anion

Negative Formal Charge

Electron Donor

H+ (proton) Acceptor

Nucleophile

Usually a Base —> Add H to make CA

Weak CA (high pKa) = Strong Base

Alkane

pKa = 50

Alkene

pKa = 44

Ammonia/Amino Radical

pKa = 35

Alkyne

pKa = 25

Alcohols/Water

pKa = 16

Ammonia Attached to C

pKa = 11

Ester Attached to Alcohol

pKa = 10

Thiol

pKa = 10

Nitrile

pKa = 9

Carboxylic Acid Attached to Alcohol

pKa = 6

Carboxylic Acid Attached to C

pKa = 5

Hydrofluoric Acid

pKa = 3

Nitric Acid

pKa = -1

Hydronium/Oxonium Ion

pKa = -2

Sulfuric Acid

pKa = -5

Hydrochloric Acid

pKa = -7

Hydrobromic Acid

pKa = -9

Hydroiodic Acid

pKa = -10