cis-1,5-Dimethyl-2,4-dinitro-2,4-diazabicyclo[3.2.0]heptan-3-one and cis-1,5-Dimethyl-2,4-dinitro-2,4-diazabicyclo[3.1.0]hexan-3-one

The title compounds, C₇H₁₀N₄O₅ (I) and C₆H₈N₄O₅ (II), each consist of a five-membered ring fused to a smaller ring. In compound (I), the C-C bridging bond distance [1.571 (4) Å] is longer than the expected distance of 1.54 Å for a C-C bond in a cyclobutane ring. In compound (II), however, the corresponding C-C bridging bond distance [1.507 (5) Å] is consistent with the expected bond length (1.51 Å) in a cyclopropane ring. The increase in the C-C bridge distance in compound (I) is most likely due to steric effects resulting from the additional methyl substituents.

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