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The complete determination of the crystal structure of solid nitromethane has been obtained from single crystal x-ray diffraction and neutron powder diffraction data. The structure is orthorhombic, space group P212121 with a=5.1832 Å, b=6.2357 Å, c=8.5181 Å at T=4.2 K, and Z=4. Two models were used to describe the thermal motion of the methyl group, one with anisotropic temperature factors for the hydrogen atoms constrained to correspond to a threefold rotation around the C–N bond, and the other treating the group as a rigid body, with a tortional oscillation about the C–N bond axis.

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If a powder pattern consists of well resolved peaks, and if it is adequately described by a crystallographic model, as determined by statistical tests, the estimates of the parameters and their standard deviations will not be significantly different, in a statistical sense, whether the method of refinement uses peak profiles or integrated intensities. If the model does not fit adequately, the standard deviations cannot be calculated by statistical methods. If peaks overlap, there are correlations between the intensities of the individual peaks that are handled automatically in the profile method, but must be included explicitly in the integrated‐intensity method. A background function should be included in the model, and its parameters refined. The background parameters have correlations with other parameters that become important if the pattern is complex, and therefore poorly resolved.

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