Some experimental aspects of absolute configuration determination using single crystal X-ray diffraction

Thompson, Amber L.; Jenkinson, Sarah F.; Fleet, George W. J.

doi:10.1016/j.tetasy.2017.08.016

Cited by 7 publications

(3 citation statements)

References 28 publications

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“…The molecule crystallized in the triclinic system and the crystal structure ( Figure 1) could be solved to a modest agreement factor R = 7.0%, the pertinent details being summarized in the Experimental Section. Of course all hydrogen atoms could be found in difference Fourier synthesis, but the crystal resulted to have P-1 symmetry, which is a centrosymmetric space group [11] thereby precluding the determination of Flack [12] or Hooft [13,14] parameters to ascertain its AC.…”

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confidence: 99%

Difficulties to Determine the Absolute Configuration of Guaiaretic Acid

Ortega

Burgueño‐Tapia

Joseph‐Nathan

2018

Natural Product Communications

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An account of the difficulties to determine the absolute configuration (AC) of guaiaretic acid (1a), using contemporary methodology, is described in commemoration of the century of its structure elucidation. In fact, the herein studied molecule was the derived diacetate 1b, since the natural lignan slowly decomposes upon manipulation. Single crystal X-ray diffraction of 1b demonstrated the structure, but calculation of Flack and Hooft parameters to know the AC was unsuccessful since the crystals were triclinic, P-1, which is a centro-symmetric space group. In turn, manual band to band comparison of experimental and DFT B3LYP/DGDZVP calculated VCD spectra of 1b allowed ascertaining its AC, although automatic comparison using the CompareVOA software was not very successful. This behavior is associated to the fact that the studied molecule has a sole stereogenic center located on the acyclic portion of a carbon chain possessing two quite similar substituents. The behavior is discussed in relation to cases where the molecular flexibility also generates a very large number of conformers.

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confidence: 99%

Difficulties to Determine the Absolute Configuration of Guaiaretic Acid

Ortega

Burgueño‐Tapia

Joseph‐Nathan

2018

Natural Product Communications

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“…Data were collected with acquisition times of 4, 8, 16, 32, 64 and 128 s/ , all on the same crystal in the same orientation to ensure the corrections were the same. The effect of collecting data at low temperature is well understood [see Goeta & Howard (2004) and Thompson et al (2017) for examples], so this was not part of this study. To avoid strain effects caused by low temperature and to ensure a large range of intensities over the range, data were collected at 250 K.…”

Section: Data Collectionmentioning

confidence: 99%

“…A similar study was carried out on pseudo-centrosymmetric 1-deoxy-l-arabinitol (Thompson et al, 2017), where the target was specifically the Flack x parameter and its associated standard uncertainty. Data sets were collected with the point groups 4/m, 4, 2 and 1, giving MoO values of 2.6, 3.4, 5.9 and R int calculated for tetraphenylene data collected with the point groups 2/m, 1 and 1 (shown in parentheses for the longest data set) collected with different acquisition times.…”

Section: The Effect Of Moo and Acquisition Timementioning

confidence: 99%

The role of multiple observations in small-molecule single-crystal service X-ray structure determination

Williams

Thompson

Watkin

2019

Acta Crystallogr Sect B

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herein are an extension of studies carried out by AEW as an undergraduate project student in 2002, since when attempts to make contact have been unsuccessful. In her absence, ALT and DJW wish to acknowledge her contribution and inspiration, understanding that responsibility for any errors is entirely theirs.In order to gain a better understanding of how to improve the quality of smallmolecule single-crystal X-ray diffraction data achievable in a finite time, a study was carried out to investigate the effect of varying the multiplicity, acquisition time, detector binning, maximum resolution and completeness. The results suggest that, unless there are strong arguments for a different strategy, a good routine procedure might be to optimize the conditions necessary to get the best data from single scans, and then choose a multiplicity of observations (MoO) to utilize the available time fully. Different strategies may be required if the crystal is highly absorbing, is larger than the incident beam, is enclosed in a capillary tube or is unusual in some other way. The signal-to-noise ratio should be used with care, as collecting data for longer or at higher multiplicity appears to give a systematic underestimate of the intensity uncertainties. Further, the results demonstrate that including poor-quality data in a refinement may degrade the result and, in the general case, the accidental omission of reflections has a very small impact on the refinement as long as they are omitted at random. Systematic omission of reflections needs a convincing procedural justification.

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X‐Ray Crystallography for Stereochemical Elucidation

Morel

Burrow

2023

Chiral Separations and Stereochemical Elucidation

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Some experimental aspects of absolute configuration determination using single crystal X-ray diffraction

Cited by 7 publications

References 28 publications

Difficulties to Determine the Absolute Configuration of Guaiaretic Acid

Difficulties to Determine the Absolute Configuration of Guaiaretic Acid

The role of multiple observations in small-molecule single-crystal service X-ray structure determination

X‐Ray Crystallography for Stereochemical Elucidation

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