Amaro Hernández AG, Rodríguez Tzompantzi T, Dávila García Á, Meza-León RL, Bernès S. Ethyl (3
S)-3-[(3a
R,5
R,6
S,6a
R)-6-hydroxy-2,2-dimethyltetrahydrofuro[4,5-
d][1,3]dioxol-5-yl]-3-{(3
S)-3-[(3a
R,5
R,6
S,6a
R)-6-hydroxy-2,2-dimethyltetrahydrofuro[4,5-
d][1,3]dioxol-5-yl]-5-oxoisoxazolidin-2-yl}propanoate chloroform monosolvate.
IUCRDATA 2020;
5:x200788. [PMID:
36340615 PMCID:
PMC9462232 DOI:
10.1107/s2414314620007889]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2020] [Accepted: 06/10/2020] [Indexed: 12/04/2022] Open
Abstract
The Flack and Watkin 2AD plot based on 1941 acentric Friedel pairs for the title chloroform solvate shows that the observed intensity differences for Friedel opposites are dominated by random and systematic errors, erasing information about resonant scattering.
The title compound, C22H33NO12·CHCl3, was obtained as a product of a double aza-Michael addition of hydroxylamine on a Chiron with a known absolute configuration. The enantiopure compound crystallized as a chloroform solvate, in space group P1, and diffraction data were collected at room temperature with Ag Kα radiation. The Flack parameter refined to x = −0.01 (16); however, the Flack and Watkin 2AD plot clearly shows that differences between Friedel opposites (the D component of the plot) do not carry any reliable information about resonant scattering of Cl atoms, and are rather dominated by random and systematic errors. The RD factor calculated using 1941 acentric Friedel pairs is RD = 0.995. On the other hand, the 2A component of the plot, related to average intensities of Friedel pairs, shows that data are of good quality (RA = 0.069). This example illustrates that while using Ag Kα radiation (λ = 0.56083 Å), scatterers heavier than Cl should be present in a chiral crystal in order to determine confidently the absolute structure of the crystal.![]()
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