Unprecedented Cyclic Isomer of Triazenes: A Computational Identification

Isomerism is very important in chemistry. Over the past 65 years, the energy‐rich N 3 R 3 family has received considerable attention both experimentally and computationally. Up to now, four isomeric types of N 3 R 3 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 N 3 H 3 —the simplest N 3 R 3 system, we unexpectedly found a new structural type V , which contains a N 3 three‐membered ring with one nitrogen‐nitrogen dative bond in the ring (i.e., cyclic ammonia‐nitrene interaction). Of all the N 3 H 3 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.