1-Methyl-4H-3,1-benzoxazine-2,4(1H)dione

In its crystal structure, the title compound, C9H7NO3, forms π-stacked dimers, with a centroid–centroid distance of 3.475 (5) Å between the benzenoid and the 2,4 dicarbonyl oxazine rings. These dimers then form staircase-like linear chains through further π-stacking between the benzenoid rings [centroid–centroid distance of 3.761 (2) Å]. The methyl-H atoms are disordered due to rotation about the C—N bond and were modeled with equal occupancy.


Structure Reports Online
The title compound is a planar molecule (Fig. 1). The bond distances are consistent with an aromatic system. The packing diagram, (Fig. 2) shows the aromatic rings form pi stacked dimers between the benzenoid ring and the 2,4 dicarbonyl oxazine ring, 3.475 (5) Å for both centroid to centroid distances (Crystalmaker ver. 2.1.2). The dimer forms a staircase-like linear chain through additional pi stacking between the benzenoid rings (3.761 (2) Å centroid to centroid).

Experimental
During the course of the reaction of N-substituted isatoic anhydrides and 2-chloroethylamine hydrochloride, unreacted 1 was isolated from products via silica gel chromatography in a 98:2 dichloromethane/methanol mobile phase. The 98:2 eluent was slowly evaporated to produce colorless rods and blocks of 1. A block was chosen for X-ray analysis, the rods gave the same unit cell as the block.

Refinement
The structure was solved using direct methods. The hydrogen atoms were positioned geometrically. A small improvement in the refinement occurred when the methyl hydrogens were modeled as 50% disordered due to free rotation about the C-N bond. Fig. 1. Thermal ellipsoid plot at 50% probability, the disordered hydrogen atoms were removed for clarity.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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.