The pKa is defined as -logKa, and indicates the degree of acidity of the hydrogens of an organic compound.

A hydrogen is all the more acid the lower its pKa.

The list begins with the compounds with the lowest acidity, the highest pKa, such as alkanes (pKa = 50). The hydrogens with respect to esters, amides, carboxylic acids, aldehydes, ketones... present an intermediate acidity with pKa values ​​between 20 and 30. The protonated species have hydrogens with negative pKas, reaching values ​​below -10 .