Dimethyl 2-(methylaminomethylene)malonate

In the title compound, C7H11NO4, which is an example of a push–pull alkene, a network of N—H⋯O and C—H⋯O interactions helps to establish the crystal structure. The investigated crystal turned out to be a non-merohedral twin with a ratio of twin components of 0.442 (3):0.558 (3). Two pairs of independent molecules (Z′ = 4) are linked by intermolecular N—H⋯O hydrogen bonds, forming independent chains; the chains are connected via intermolecular C—H⋯O contacts, building a three-dimensional network.


Related literature
Chemical and physical properties of the title related structures were recently discussed (Gróf et al., 2008 and literature cited therein).
The study of a similar compound, dimethyl 2-(aminomethylene)malonate, (Gróf et al., 2008) revealed that this structure exists in the solid phase as EZ conformer (E denotes away from C=C double bond orientation of the carbonyl oxygen in trans position; Z denotes towards to C=C double bond orientation of the carbonyl oxygen in cis position). The title compound exists in the solid phase as ZZa conformer (a denotes anti orientation of the methylamino group, e.g. away from the C=C double bond orientation).
The molecules I and II, and molecules III and IV of the title compound ( Fig.1) show pseudo translation (Kálmán & Argay, (1998).

Experimental
To dimethyl 3-methoxymethylenemalonate (1.74 g, 10 mmol) in methanol (10 ml), an aqueous solution of methylamine (12 mmol) was added dropwise (amount according to concentration and density) over a period of 30 min with stirring.
The slightly warmed mixture was stirred overnight at room temperature. The reaction mixture was then briefly heated to reflux (ca. 20 min). After ensuring that no starting derivative remained (thin-layer chromatography; Silufol 254, Kavalier Czechoslovakia; eluent chloroform-methanol 10:1 v/v, detection UV light 254 nm), the reaction mixture was evaporated on a vacuum evaporator and chromatographed on silica gel (eluent dichloromethane-methanol 10:1 v/v). Obtained product was recrystallized from minimal amount of chloroform and n-hexane mixture in refrigerator.
The solid phase mid-IR vibrational spectrum was recorded with a Nicolet model NEXUS 470 FTIR spectrometer at room temperature. The measurement was performed after mixing the powdered sample with KBr into a pellet.

Refinement
Olefinic and amino H atoms were positioned geometrically and allowed to ride on their corresponding parent atoms at distances of 0.93 and 0.86 Å, respectively, with U iso (H) = 1.2U eq (C,N). Methyl H atoms were located in a difference Fourier map and included in the model as a rigid rotating group, with C-H distance of 0.96 Å and with U iso (H) = 1.5U eq (C).
For the refinement the reflection data file was modified using the program HKLF5 (Bolte, 2004). The contribution of the minor twin component refined to 0.442 (3). Fig. 1. The atom-numbering scheme of dimethyl 2-(methylaminomethylene)malonate. Displacement ellipsoids are drawn at the 60% probability level.

Special details
Experimental. face-indexed (CrysAlis RED;Oxford Diffraction, 2006). 96 rigid bond restaints (DELU) were used in the refinement because the data to parameter ratio is low due to four independent molecules in the twinned structure. 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.