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The crystal structure of 5-aminolevulinic acid hydrochloride (systematic name: 4-carboxy-2-oxobutan-1-aminium chloride), C 5 H 10 NO 3 + ·Cl − , has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory (DFT) techniques. The structure is compared to a recent single-crystal determination Wang et al. (2025). Z. Kristallogr. New Cryst. Struct. 240 , 413–414. 5-Aminolevulinic acid hydrochloride crystallizes in the space group Pbca (No. 61), with a = 8.20862 (9), b = 11.22253 (10), c = 16.8595 (2) Å, V = 1553.12 (4) Å 3 , and Z = 8 at 298 K. The crystal structure consists of layers parallel to the ab plane. The center of the layers contains hydrophilic NH 3 , Cl, and CO 2 H groups, and the outer surface of the layers is composed of hydrophobic CH 2 groups. Hydrogen bonds are prominent in the crystal structure. The ammonium group acts as a donor to three chloride anions, and one hydrogen bond is bifurcated to the carbonyl group. Each Cl − anion is an acceptor in three N—H...Cl hydrogen bonds, plus one from the carboxylic acid group. These hydrogen bonds connect the cations and anions into the layers parallel to the ab plane. The powder pattern has been submitted to the International Centre for Diffraction Data (ICDD) for inclusion in the Powder Diffraction File (PDF)
Ducreux et al. (Fri,) studied this question.