Ring closure of appropriately beta-substituted nitrosamines leads to the formation of dihydrooxadiazolium ions. These relatively stable, crystalline compounds react with nucleophiles, either at the position of the beta-substituent or by displacement of an alkyl group bound to the nitrogen. These compounds are intramolecular varients of alkoxydiazenium ions, which are formed by the O-alkylation of nitrosamines with a variety of agents, including alkyl-fluorosulfonates. The alkoxydiazenium ions are also stable, crystalline solids. They react with nucleophiles usually by displacement at the O-alkyl group. One exception to this, however, is the reaction of 3,4-dichlorothiopheno in organic solvents to form thioethers by O-dealkylation and N-dealkylation. The by-products of the dealkylations are the corresponding nitrosamines. The aqueous reactions of 3,4-dichlorothiophenol are slower and pH-dependent. In acidic media, 3,4-dichlorothiophenol reacts only at the O-alkyl groups, whereas in weakly alkaline media, a little O- and N-dealkylation is observed, together with considerable base-catalysed decomposition of the alkoxydiazenium ions.