Levulinic acid

The title compound (systematic name: 4-oxopentanoic acid), C5H8O3, is close to planar (r.m.s. deviation = 0.0762 Å). In the crystal, the molecules interact via O—H⋯O hydrogen bonds in which the hydroxy O atoms act as donors and the ketone O atoms in adjacent molecules as acceptors, forming C(7) chains along [20-1].

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FF2114).

Comment
Levulinic acid [systematic name: 4-oxopentanoic acid], (I), is a biogenic product of hexose acid hydrolysis at elevated temperatures that can be obtained from renewable resources. This functionalized carbon structure is widely used as chemical intermediate in the manufacture of fuel extenders, biodegradable polymers, herbicides, antibiotics, flavours and useful 5-carbon compounds (Timokhin et al., 1999;Reichert et al., 2010). Levulinic acid was investigated in a continuation of our studies of the IR spectra of hydrogen bonding in carboxylic acid derivatives (Flakus & Stachowska, 2006;Flakus & Hachuła, 2008). In order to study interactions occurring via hydrogen bonds and molecular packing in this compound, we have now determined the structure of (I) using diffraction data collected at 100 K.
The monoclinic structure of (I) is composed of molecular sheets stacked along [101] direction. Atom O1 of the carboxylic group acts as a hydrogen-bond donor via H1 to carbonyl atom O3 belonging to the acetyl group of adjacent molecule.

Experimental
Levulinic acid was purchased from Aldrich-Sigma. Crystals of title compound, suitable for X-ray diffraction, were selected directly from purchased sample.

Refinement
The H atoms were introduced in geometrically idealized positions and allowed for with an appropriate riding model with C-H distances of 0.99 Å (CH 2 ) and U iso (H) values set at 1.2U eq (C) or 0.98 Å (CH 3 ) and with U iso (H) values set at 1.5U eq (C). The H atom which takes part in hydrogen bonding was located in a difference Fourier map and was refined with U iso (H) value set at 1.5U eq (O).

Computing details
Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2010).    Part of the crystal structure of (I), viewed along the a axis, showing the C(7) chains. The red lines indicate the hydrogenbonding interactions. For the sake of clarity, all H atoms bonded to C atoms were omitted. 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.