Polynitrogen compounds, comprising only nitrogen atoms, are rare. They are considered as promising candidates of clean (green) high energy density materials because of their high energy content and their sole decomposition product is N-2. Extending the previous work which was on cyclic N-8 isomers, in this study some cyclic N-10 isomers having 1-4 cycles are considered within the limitations of density functional theory at the levels of B3LYP/6-311++G(d,p) and B3LYP/cc-PVTZ. Some of the structures, including the monocyclic one, decompose by eliminating certain number of N-2 units while some remain intact. All the stable isomers (1-3, 6-8) investigated presently are highly endothermic that they are candidates for clean high energy materials. Certain quantum chemical properties, IR and UV-VIS spectra as well as the specific impulse values for the stable structures are reported. (C) 2018 The Author. Published by Elsevier Ltd.