pKa = −log(Ka). A lower pKa means a stronger acid — it dissociates more completely.

Each unit of pKa represents a factor of 10 in acid strength. An acid with pKa 5 is 10 times stronger than one with pKa 6, and 100,000 times stronger than one with pKa 10.

Basicity is the mirror image. The weaker the conjugate acid (higher its pKa, in the pKaH notation used for amines below), the stronger the base. There is no separate “pKb table” in this appendix — every base’s strength is read from the pKa of its conjugate acid.

A functional group is a moderate acid, base, both, or neither, depending on which factor from Chapter 3 applies to it — resonance, electronegativity, induction, or hybridization. The tables below are grouped by compound class so those factors can be compared side by side.

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