Bis(2,2-dinitropropyl)formal

The complete molecule of the title compound [systematic name: bis(2,2-dinitropropoxy)methane], C7H12N4O10, which was synthesized by the condensation reaction between 2,2-dinitropropanol and paraformaldehyde in methylene chloride, is generated by crystallographic twofold symmetry with one C atom lying on the rotation axis. In the crystal structure, molecules are linked into chains running parallel to the b axis by intermolecular C—H⋯O hydrogen-bond interactions, generating rings of graph-set motif R 2 2(14).

The complete molecule of the title compound [systematic name: bis(2,2-dinitropropoxy)methane], C 7 H 12 N 4 O 10 , which was synthesized by the condensation reaction between 2,2dinitropropanol and paraformaldehyde in methylene chloride, is generated by crystallographic twofold symmetry with one C atom lying on the rotation axis. In the crystal structure, molecules are linked into chains running parallel to the b axis by intermolecular C-HÁ Á ÁO hydrogen-bond interactions, generating rings of graph-set motif R 2 2 (14).

Comment
The title compound is an important energetic material used in propellant and explosive formulations (Garver et al. 1985;Hamilton & Wardle, 1995). It was also combined with liquid bis(2,2-dinitropropyl)acetal (BDNPA) to prepare the BDNPF/A energetic plasticizer (Adolph, 1991;Hamilton & Wardle, 1997). Here we report the crystal structure of the title compound.

Experimental
The title compound was synthesized by reacting 2,2-dinitropropanol (6.0 g) with paraformaldehyde (0.6 g) in the presence of concentrated sulfuric acid as catalyst in methylene chloride below 5°C. Single crystals suitable for X-ray analysis were obtained by slow evaporation of a diethyl ether/mineral ether (1:6 v/v) solution.

Refinement
All non-H atoms were refined with anisotropic atomic displacement parameters. All H atoms were positioned geometrically and refined using a riding model, with C-H =0.96-0.97 Å and with U iso (H) = 1.2 U eq (C) or 1.5 U eq (C) for methyl H atoms.
Figures Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. Atoms labelled with the suffix 2 are generated by the symmetry operator (1-x, y, 1/2-z).
Bis ( Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.