Thermal decomposition of a 1: l mixture of (CH, OCO), C (N,), and (CD, OCO), C (N,), to yield l-methyl-5-carbomethoxytetrazole-d, proceeds with crossover of the isotope label, indicating an intermolecular pathway for this reaction. A chain mechanism involving tetrazolium nucleophiles is proposed. The thermal decomposition of diazidomalonamide (14) and N, N'- dimethyldiazidomalonamide (1 6) occurs analogously yielding 5-carbamoyltetrazole (15) ...