The crystal structures of four nitroheptitols obtained fromd-galactose andd-glucose by a Fischer-Sowden reaction,i.e., 7-deoxy-7-nitro-l-glycero-l-galacto-heptitol monohydrate, 7-deoxy-7-nitro-d-glycero-l-galacto-heptitol, 7-deoxy-7-nitro-d-glycero-l-gulo-heptitol, and 1-deoxy-1-nitro-d-glycero-d-gulo-heptitol, were determined by X-ray diffraction using direct methods. Thel-glycero-l-galacto and thed-glycero-l-gulo isomers adopt the expected conformations, one having the extended planar zig-zag geometry and the other being bent to a sickle. Remarkably, the other two compounds havingd-glycero-l-galacto andd-glycero-d-gulo configurations showed extended planar conformations, both of them thus tolerating a parallel 1,3-interaction between oxygens (O//O). In all compounds, the oxygen atoms of the nitro group show a preference in their orientations to the hydrogen atoms at C-1 and C-2, one found in a position synclinal to H-12 and the other 1,3-synclinal to H-2.