A Practical Approach to Teaching Resonance in Introductory Organic Chemistry

Resonance theory is a powerful concept that when applied qualitatively can be extremely useful to students of organic chemistry, particularly for understanding chemical reactivity. However, students often struggle with the concept of resonance and are unable to fully exploit its utility because they do not recognize molecules that exist as resonance hybrids. Furthermore, students frequently are unable to generate all, or the most important, canonical forms associated with organic molecules with resonance. A practical, instructional approach to identifying organic molecules that exist as resonance hybrids, along with a step-by-step strategy for drawing the important resonance contributors is presented. The process lays out criteria for molecules with resonance and utilizes a seven-step algorithm for identifying molecules that exist as resonance hybrids. Once molecules with resonance are identified, and classified into categories (A, B and C), a detailed process for drawing canonical forms, using the curved arrow convention for each category of molecule is presented. Numerous examples are included to illustrate the process.