(2,2-Dimethyl-1,3-dioxolan-4-yl)methyl 3-carboxypropanoate

In the title compound, C10H16O6, the five-membered ring has an envelope conformation. The packing involves hydrogen-bonded carboxylic acid inversion dimers and three C—H⋯O interactions.

In the title compound, C 10 H 16 O 6 , the five-membered ring has an envelope conformation. The packing involves hydrogenbonded carboxylic acid inversion dimers and three C-HÁ Á ÁO interactions.

Comment
Isopropylidene groups are often used as protecting or activating units in polyhydroxyalkyl compounds used for synthesis of sugar-like derivatives; for a brief introduction and the structure of a related derivative, see the accompanying paper (Kuś et al., 2009).
Hemi-esters of succinic acid are often used for the synthesis of amphiphilic compounds with well organized structure (Osanai et al., 1997). Non-symmetrical esters of succinic acid have been used for the synthesis of prodrugs that release the corresponding drugs very slowly; e.g. steroid drugs (Scriba, 1995) or Phenytoin (Scriba, 1993). Solketal (D,L-isopropylideneglycerol, Aldrich) was used for the synthesis of compound 1.
The molecule of compound 1 is shown in Fig. 1. Bond lengths and angles may be regarded as normal. The chain C2 through to C7 has an approximately extended conformation (absolute torsion angles between 158 and 174°). The fivemembered ring displays an envelope conformation, with local mirror symmetry about C8 and the midpoint of C6-C7.
The molecular packing (Fig. 2) is dominated by the formation of the well known carboxylic acid dimers via classical hydrogen bonding. Three further contacts, of the type C-H···O, link the molecules to a three-dimensional pattern.

Refinement
The OH hydrogen was refined freely. Methyl H atoms were identified in difference syntheses and refined as idealized rigid groups (C-H 0.98 Å, H-C-H 109.5°) allowed to rotate but not tip. Other H atoms were included at calculated positions and refined using a riding model, with fixed C-H bond lengths of 0.95 Å (CH, aromatic), 0.99 Å (CH 2 ) and 1.00 Å (CH, sp 3 ); U iso (H) values were fixed at 1.2U eq of the parent C atom (1.2U eq for methyl H).
The atom C6 is disordered over two sites with occupancy ratio 0.9:0.1, corresponding to a second conformation of the five-membered ring. An appropriate set of similarity restraints was used to ensure stability of refinement.  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.