Relative acidity/basicity of molecules with varying pKa values, and approximate pKa values for common functional groups
| Acidic Groups | pKa Value | Basic Groups | pKa Value |
|---|---|---|---|
| Sulfonic acids | <1 | Aliphatic amines | 8–11 |
| Phosphonates | 2 | Saturated nitrogen heterocycles | 9–11 |
| Carboxylic acids | 2.5–5 | Pyridines | 4–6 |
| Imides | 8–11 | Anilines | 3–5 |
| Thiols | 7–10 | ||
| Sulphonamides | 8–10 | Weak base | 4.5–9.5 |
| Phenols | 8–10 | Very weak base | 0.0–4.5 |
| Weak acid | 4.5–9.5 | ||
| Very weak acids | 9.5–14 |