A laboratory experiment was designed for undergraduate students, in which the outcome of an easy single-step organic synthesis with well-defined conditions was not elucidated until the end of the exercise. In class, students predict and discuss the possible products using their knowledge of reaction mechanisms. In the laboratory, they learn how to carry out a reaction safely with gaseous isobutene, and to isolate and identify the two main products. The class and the laboratory components are completed in 10 h, including laboratory time of 6 to 7 h, divided in two sessions. The class-component could also be implemented independently as a theoretical exercise in a "virtual experiment" simply by presenting the methods and results to students using a guided-inquiry approach, appropriate for a standard 3 h undergraduate class. The finding that the simple reaction leads to a largely unexpected product, together with open discussions with students covering several theoretical aspects applicable to this reaction, helps to promote critical thinking and to provide an effective educational tool to better understand the process of scientific research in chemistry.