As part of a series of investigations of molecules with large numbers of nitro groups, the structures and properties of nitroformic acid, NO2CO2H, nitroformyl nitrate, NO2C(O)ONO2, and the ion pair ammonium nitroformate, NH4NO2CO2, have been determined using GX theories (X = 2, 3, 4). Minimum-energy structures, vibrational frequencies, selected bond energies, and enthalpies of formation were determined. The title substances may not have much application as high energy materials like other high-nitro compounds, but they may act as good nitrating agents since certain bonds in the molecules are of low enough energy to suggest high reactivity.