Seeks to understand elementary reaction types as a function of chemical structure by emphasizing organic compounds. Topics include acid-base, nucleophilic substitution, oxidation-reduction, electrophilic addition, elimination, conformational analysis, stereochemistry, aromaticity, and molecular spectroscopy. CHEM 1821, 2411, or 2311 may be taken concurrently or after completing CHEM 1820. Drop or withdrawal from CHEM 1820, requires drop/withdrawal from CHEM 1821/2411/2311.