Illustrated Glossary of Organic Chemistry

Structure-Activity Relationship (SAR): The study of the relationship between a drug's molecular structure and the drug's biological activity. Structure-activity studies are critical to designing a pharmaceutical with the greatest potency and least side effects.

These molecules illustrate the relationship between a sulfa drug's heterocycle and the pK_a of the sulfonamide NH proton, a factor important to effective antibiotic performance.