Azide derivatives of the three possible (two angular and one linear) naphtho-as-triazines 7a, loa, and 15a were prepared and the equilibria leading to fused tetrazoles were investigated by NhfR spectroscopy and X-ray analysis. Comparison of the differently annelated systems (topological isomers) revealed an essential" annelation effect": while 3-azidonaphtho [2, 1-c]- m-triazine (7a) and 3-azidonaphtho [1, 2-c]-as-triazine (loa) formed" b-fused" tetrazoles 7b ...