Deprotonation from nitrogen of the aci-nitro tautomer (4) of nitramide (1) has been shown to give an anion which does not correspond to an energy minimum on the potential energy surface. The base-catalysed decomposition of nitramide via this tautomer, therefore, occurs by an enforced concerted mechanism which, on the basis of previously reported experimental results, is deduced to be highly asynchronous. Protonation of 4 on the hydroxy also leads to an ion which spontaneously fragments, consequently the acid-catalysed decomposition of 1 via 4 also involves concerted proton transfer and fragmentation. The uncatalysed decomposition of nitramide through the same tautomer 4 is also concerted, and the mechanism through a cyclic transition structure involving two water molecules is shown to be more favourable than a cyclic concerted mechanism involving a single water molecule. Structures and energies of all relevant species have been calculated and shown to be in good agreement with experimental results where these are available.