A combined computation, kinetic, and trapping study of the 2,5-didehydropyridine biradical finds the hydrogen abstraction reaction to be tunable by protonation. The observation of small amounts of pyridine products in the thermolysis of a C,N-dialkynylimine, or azaenediyne, only when the reaction occurs in the presence of moderate amounts of protic acid, is consistent with qualitative theoretical predictions as well as ab initio calculations at the CASSCF and CASMP2 levels. The implication of these findings for a more selective antitumor agent is discussed.