Priority and Selectivity Rules To Help Students Predict Organic Reaction Mechanisms

Organic reaction mechanisms lie at the heart of developing an understanding of how the molecular world functions. However, many students simply try to memorize mechanisms, or use their knowledge of the reagent and product to create a mechanism that “works”. This is not helped by the content-heavy organic chemistry curriculum which focuses on rapidly progressing through a range of reaction types and functional groups. For some students, especially nonchemistry majors, OrgChem101 becomes a “rite of passage” to be endured, learned and forgotten. This paper presents an alternative way of introducing students to organic reaction mechanisms, in which mechanistic rationale and thinking is explicitly taught to students, in a simple logical way, before they meet any specific reactions. In particular, to facilitate this, a series of “priority rules” have been developed. These priority rules help students find reactive sites and predict curly arrow mechanisms, even when faced with previously unseen reagents. This approach is designed to empower students to think about organic molecules in a different way, focusing on reactivity and structure. This enables students to realize that they can predict reactions of which they have no prior knowledge by proposing plausible mechanisms from first principles. This approach to mechanistic teaching sits alongside contextualized examples and allows students to rapidly see how the principles they are learning can help them solve real-world problems─ensuring that they develop not only a mechanistic view of the molecular world but also a motivation to learn more.