Unprecedented Cyclic Isomer of Triazenes: A Computational Identification

AbstractIsomerism is very important in chemistry. Over the past 65 years, the energy‐rich N3R3 family has received considerable attention both experimentally and computationally. Up to now, four isomeric types of N3R3 have been identified, i.e., triazenes I, triimides II, iso‐triazenes III, and cyclo‐triazanes IV. In this work, via the composite CBS‐QB3 study on the isomers and transition states of N3H3—the simplest N3R3 system, we unexpectedly found a new structural type V, which contains a N3 three‐membered ring with one nitrogen‐nitrogen dative bond in the ring (i.e., cyclic ammonia‐nitrene interaction). Of all the N3H3 isomers, V lies the highest in energy (78.7 kcal/mol above the global triazene) and possesses a relatively low conversion barrier 8.9 kcal/mol. Yet quite promisingly, suitably choosing substituents can tune the rate‐determining barrier of V to reach around 20 kcal/mol. Thus, synthesis of the newly found triazene isomer V is highly probable.