3-Carbamoyl-2,2-dimethylcyclopentane-1,1-dicarboxylic acid

In the title compound, C10H15NO5, the five-membered cyclopentane ring has an envelope conformation, with four atoms lying in a plane (mean deviation = 0.0213 Å), while the fifth atom deviates from this plane by 0.626 (2) Å. A three-dimensional structure is formed through N—H⋯O and O—H⋯O hydrogen bonds between the amide and carboxylic acid groups and both carboxylic acid and amide O-atom acceptors.

In the title compound, C 10 H 15 NO 5 , the five-membered cyclopentane ring has an envelope conformation, with four atoms lying in a plane (mean deviation = 0.0213 Å ), while the fifth atom deviates from this plane by 0.626 (2) Å . A threedimensional structure is formed through N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds between the amide and carboxylic acid groups and both carboxylic acid and amide O-atom acceptors.
In the structure of (II) (Fig. 1), the five-membered C1-C5 ring has an envelope conformation, which is typical for this class of compounds. The C1-C3-C4-C5 atoms lie in a plane (mean deviation, 0.0213 Å) while C2 deviates from this plane by 0.626 (2) Å. The bond lengths C1-C2 and C2-C3 [1.5707 (16) and 1.5752 (17) Å respectively] are somewhat longer than the normal single Csp 3 -Csp 3 bond length. Other C-C bond lengths observed in this compound are unremarkable and fall in the range of 1.5285 (19)-1.5489 (16) Å. A three-dimensional network structure is formed through intermolecular N-H···O hydrogen bonds between the amide and carboxyl groups and O-H···O hydrogen bonds between the carboxylic acid groups and amide O-atom acceptors (Table 1).

Experimental
The synthesis of the cyclic anhydride (I) (Fig. 2) was carried out according to the method described by Polonski (1983).
Compound (I) (1.00 g, 4.36 mmol) was added in three portions to the cooled (-40 °C) saturated solution of ammonia in methanol (10 ml). The resulting solution was stirred for 1 h and white needles formed during this period were filtrated off. These needles can be easily dissolved in water. The mother liquor was acidified with dilute hydrochloric acid to pH 3 and allowed to stand for 24 h. The resulting white needles of the title compound were collected by filtration.  3421,3328,3254,3008,2976,2941,2777,2595,1737,1721,1651,1551,1263,1242,1207,637.

Refinement
Carboxylic acid and amide H atoms were located in a difference Fourier synthesis and both positional and displacement parameters were allowed to refine. Other H atoms were positioned geometrically, with C-H = 0.96-0.98 Å and were allowed to ride on their parent atoms, with U iso (H) = 1.2U eq (methine or methylene C) or 1.5U eq (methyl C). In the absence of a suitable heavy atom, the absolute configuration of the title compound could not be determined (1146 Friedel pairs).

Figure 1
The molecular structure and atom numbering scheme for the title compound, showing 50% probability displacement ellipsoids.

Figure 2
The synthetic route to the title compound (II). 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 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.