This article investigates how understanding the theory of organic chemistry facilitates the total synthesis of organic compounds. After locating the philosophical significance of this question within the methodology or epistemology of applied science, I summarize the results of previous work on this issue—roughly that theoretical organic chemistry underwrites a sequence of heuristic policies that help to isolate plausible synthetic routes from the array of possibilities provided by structural or descriptive organic chemistry. While this prior account makes a solid start, it (...) does not capture all of the ways that the theory of organic chemistry contributes to total synthesis. This article aspires to enrich this account by exploring some additional ways that theory contributes. More specifically, I investigate how understanding the theory of organic chemistry can facilitate both the development of novel synthetic reactions and the implementation of a synthetic plan. The role of theory in these aspects of total synthesis will be explored by considering a particular, novel synthesis of longifolene. (shrink)