2,5-Dioxopyrrolidin-1-yl 2-methylprop-2-enoate

In the title compound, C8H9NO4, the pyrrolidine ring (r.m.s. deviation 0.014 Å) is almost normal to the mean plane of the propenoate group (r.m.s deviation 0.028 Å), making a dihedral angle of 86.58 (4)°. In the crystal, molecules are linked via pairs of weak C—H⋯O hydrogen bonds, forming inversion dimers which stack along the c axis.

In the title compound, C 8 H 9 NO 4 , the pyrrolidine ring (r.m.s. deviation 0.014 Å ) is almost normal to the mean plane of the propenoate group (r.m.s deviation 0.028 Å ), making a dihedral angle of 86.58 (4) . In the crystal, molecules are linked via pairs of weak C-HÁ Á ÁO hydrogen bonds, forming inversion dimers which stack along the c axis.
Supporting information for this paper is available from the IUCr electronic archives (Reference: ZQ2217).

Comment
The title compound is a monomer for free radical polymerization (Batz et al., 1972) and controlled free radical (ATRP) polymerizations (Rathfon & Tew, 2008) to form homo-and copolymers. After preliminary polymerization, these polymers serve as candidates to undergo post-polymerization modification to create functional polymers (Gauthier et al., 2009). A structure determination was undertaken to investigate the possibility of free radical, topochemical polymerization of this monomer while being exposed to X-ray radiation (Matsumoto, 2003). The molecular unit is shown in Figure 1. The crystal structure reveals that no polymerization has taken place. The asymmetric unit consists of a single monomer unit packed into a monoclinic cell with a volume of 871 Å 3 . While analysis of the intermolecular contacts within the unit cell reveals a close contact of 3.487 Å between the carbons of adjacent double bonds (C6 and C8), this contact occurs between a pair of adjacent molecules but is not maintained with additional molecules in order to achieve a favorable pathway for polymerization. Figure 2 shows the packing in the unit cell. The molecule is composed of two planar regions. Least-squares planar analysis reveals r.m.s. deviation from planarity for the pyrrolidine ring of 0.014 Å and 0.028 Å for the propenoate portion. The two planes are essentially normal to each other with an angle of 86.58 (4) degrees between least-squares planes. The conformation of the methyl H atoms is found to be syn to the vinylic proton. This is the preferred configuration by approximately 2 kcal/mol (Deslongchamps & Deslongchamps, 2011).

Experimental
Crystals of the title compound, C 8 H 9 NO 4 , were grown unintentionally from slow evaporation of a solution of the compound in 1:4 ethyl acetate:hexanes at 0 °C.

Refinement
Although all of the H-atoms were located in difference maps, H-atoms were placed at idealized positions and refined with a riding model having U iso (H) = 1.2 times U eq (C).   Unit cell view along the +a axis showing the lack of proper stacking for polymerization to occur.

2,5-Dioxopyrrolidin-1-yl 2-methylprop-2-enoate
Crystal data 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 R-factors(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. CheckCIF detected one Alert level C stating that a large K value of 2.279 was detected in the Analysis of Variance. Examination of the SHELX output does reveal one large K value (1.967) for the Fc/Fc(max of 0.000). Examination of the K values as a function of resolution shows no large K values from inf to 0.83 Å. Our conclusion is that the large K value results from very weak relections in the 0.80 -0.60 A region and should have a neglibile effect upon the final structural results while the inclusion of the data would minimize termination effects in the calculation of electron density.  (7) 0.0076 (7) −0.0019 (7) C2 0.0377 (9) 0.0288 (9) 0.0328 (8) 0.0099 (7) 0.0108 (7) 0.0026 (7) C3 0.0382 (9) 0.0269 (9) 0.0264 (8) 0.0032 (7) 0.0097 (7) 0.0037 (7)  C4 0.0385 (9) 0.0254 (8) 0.0234 (7) 0.0048 (7) 0.0118 (7) 0.0025 (6)