At the most fundamental level, the ability of a chemical compound to elicit a pharmacologic/therapeutic effect is related to the influence of various physical and chemical (physicochemical) properties of the chemical substance on the biomolecule(s) that it interacts with. Among the most pharmacologically influential physicochemical properties of organic medicinal agents (OMAs) are:

1. Solubility
2. Acidity and basicity
3. Reactivity

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ACID-BASE PROPERTIES OF ORGANIC MEDICINAL AGENTS

A very important physicochemical property of OMAs is their ability to function as an organic acid and/or an organic base. Acidic and/or basic properties of OMAs are important in both pharmaceutical (dosage formulation, etc.) and pharmacological (disposition, structure at target site, etc.) phases.

The following primer will concentrate on two aspects of acid-base chemistry, (1) recognition of acidic or basic organic functional groups and (2) an estimation of the relative acid/base strength of these groups.

1. Definitions (click to see examples)
   • Acid: an organic compound containing a functional group that can donate a proton (H⁺)
   • Bases: an organic compound that contains a functional group that can accept a H⁺

2. Common acidic organic functional groups
   • Carboxylic acid (-COOH)
   • Phenol (Ar-OH)
   • Sulfonamide (R-SO₂NH₂)
   • Imide (R-CO-NH-CO-R)

3. Common basic organic functional groups
   • Aliphatic 1º (R-NH₂), 2º (R₂NH) and 3º (R₃N)-amines
   • Heterocyclic amines (click for examples)
   • Aromatic amines (Ar-NH₂)

4. Estimating Relative Acid/Base Strength
   • Click here for a chart comparing acid/base strengths.
   • Click here for a chart comparing acid strengths of various functional groups.
   • Click here for a chart comparing base strengths of various functional groups.

5. Ionization of Acidic and Basic Functional Groups (Click for reactions)

6. Acidic and Basic Functional Group Salt Formation (Click for reactions)

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