This article is an approach to the historical development of the structural elucidation of organic natural substances that began with chemical degradations, isotopic labeling processes and sometimes synthesis, all chemical reactions. We used the work of Lavie et al. in: “Constituents of Withania somnifera Dun. III. The side chain of Withaferin A” as the study-object, complemented by other bibliographic material, and we proposed mechanistic routes of each reaction used by the authors. The objective was to explain these processes from the didactic point of view of reaction mechanisms