The structure of zymonic acid (systematic name: 4-hy­droxy-2-methyl-5-oxo-2,5-di­hydro­furan-2-carb­oxy­lic acid), C6H6O5, which had previously eluded crystallographic determination, is presented here for the first time. It forms by intra­molecular condensation of parapyruvic acid, which is the product of aldol condensation of pyruvic acid. A redetermination of the crystal structure of pyruvic acid (systematic name: 2-oxo­propanoic acid), C3H4O3, at low temperature (90 K) and with increased precision, is also presented [for the previous structure, see: Harata et al. (1977). Acta Cryst. B33, 210–212]. In zymonic acid, the hy­droxy­lactone ring is close to planar (r.m.s. deviation = 0.0108 Å) and the dihedral angle between the ring and the plane formed by the bonds of the methyl and carb­oxy­lic acid carbon atoms to the ring is 88.68 (7)°. The torsion angle of the carb­oxy­lic acid group relative to the ring is 12.04 (16)°. The pyruvic acid mol­ecule is almost planar, having a dihedral angle between the carb­oxy­lic acid and methyl-ketone groups of 3.95 (6)°. Inter­molecular inter­actions in both crystal structures are dominated by hydrogen bonding. The common R22(8) hydrogen-bonding motif links carb­oxy­lic acid groups on adjacent mol­ecules in both structures. In zymonic acid, this results in dimers about a crystallographic twofold of space group C2/c, which forces the carb­oxy­lic acid group to be disordered exactly 50:50, which scrambles the carbonyl and hydroxyl groups and gives an apparent equalization of the C—O bond lengths [1.2568 (16) and 1.2602 (16) Å]. The other hydrogen bonds in zymonic acid (O—HO and weak C—HO), link mol­ecules across a 21-screw axis, and generate an R22(9) motif. These hydrogen-bonding inter­actions propagate to form extended pleated sheets in the ab plane. Stacking of these zigzag sheets along c involves only van der Waals contacts. In pyruvic acid, inversion-related mol­ecules are linked into R22(8) dimers, with van der Waals inter­actions between dimers as the only other inter­molecular contacts.

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Published in Acta Crystallographica Section E: Crystallographic Communications, v. 75, part 6, p. 858-862.

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

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We are thankful for research funding from the National Science Foundation under NSF CAREER award CHE-1255290 to MIG, and the MRI program, grants CHE-0319176 and CHE-1625732. An Inter­national Visiting Scholar grant from the College of Arts and Sciences at UK is gratefully acknowledged.

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Crystal structure: contains datablocks global, pyruvic, zymonic. DOI: https://doi.org//10.1107/S2056989019007072/hb7818sup1.cif

Structure factors: contains datablock zymonic. DOI: https://doi.org//10.1107/S2056989019007072/hb7818zymonicsup2.hkl

Structure factors: contains datablock pyruvic. DOI: https://doi.org//10.1107/S2056989019007072/hb7818pyruvicsup3.hkl

Supporting information file. DOI: https://doi.org//10.1107/S2056989019007072/hb7818zymonicsup4.cml

Supporting information file. DOI: https://doi.org//10.1107/S2056989019007072/hb7818pyruvicsup5.cml

checkCIF report

Supplementary crystallographic information is available on the online version of the article.

hb7818.cif (944 kB)
Crystallographic Information File (CIF). Contains datablocks global, pyruvic, zymonic.

sendsupfiles1.txt (128 kB)
Structure factor file (CIF format). Contains datablock zymonic.

sendsupfiles2.txt (115 kB)
Structure factor file (CIF format). Contains datablock pyruvic.

sendsupfiles3 (2 kB)
Chemical Markup Language (CML) file. Supplementary material.

sendsupfiles4 (1 kB)
Chemical Markup Language (CML) file. Supplementary material.