Applications and properties of the Bijvoet intensity ratio

Flack, H. D.; Bérnardinelli, Gerald

doi:10.1107/s0108767308013780

Cited by 32 publications

(29 citation statements)

References 21 publications

(25 reference statements)

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“…Then, Friedif-centro = 195 for (I)-LT (Cu K radiation) and 123 for (II)-LT (Mo K radiation). The corresponding standard uncertainties would be 0.041 and 0.065 (Flack et al, 2006;Flack & Bernardinelli, 2008). The refined values of the Flack (1983) parameter converged to 0.504 (15) and 0.41 (13) for (I)-LT and (II)-LT, respectively.…”

Section: Figure 16mentioning

confidence: 96%

“…Because of the presence of the pseudo-inversion centres that link every second molecule, a half of the content of the unit cell can be considered as centrosymmetric and, as a consequence, would lower the value of Friedif. Then the value of Friedif-centro (Flack & Bernardinelli, 2008) would be 465 for (I)-LT (Cu K radiation) and 284 for (II)-LT (Mo K radiation). However, the other set of inversion centres ( 3 4 , 0.1, 3 4 etc., see text above) is present in the structure, which would also decrease the value of Friedif-centro.…”

Section: Figure 11mentioning

confidence: 99%

“…The Friedel coverage is thus 4883/(4883 + 232) = 0.95. Flack et al (2006), as well as Flack & Bernardinelli (2008), found an estimation of the value of the standard uncertainty of the Flack parameter from the calculated value of Friedif. Because of the presence of the pseudo-inversion centres that link every second molecule, a half of the content of the unit cell can be considered as centrosymmetric and, as a consequence, would lower the value of Friedif.…”

Section: Figure 11mentioning

confidence: 99%

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High- and low-temperature phases in isostructural 4-chloro-3-nitroaniline and 4-iodo-3-nitroaniline

et al. 2014

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The structures of 4-chloro-3-nitroaniline, C6H5ClN2O2, (I), and 4-iodo-3-nitroaniline, C6H5IN2O2, (II), are isomorphs and both undergo continuous (second order) phase transitions at 237 and 200 K, respectively. The structures, as well as their phase transitions, have been studied by single-crystal X-ray diffraction, Raman spectroscopy and difference scanning calorimetry experiments. Both high-temperature phases (293 K) show disorder of the nitro substituents, which are inclined towards the benzene-ring planes at two different orientations. In the low-temperature phases (120 K), both inclination angles are well maintained, while the disorder is removed. Concomitantly, the b axis doubles with respect to the room-temperature cell. Each of the low-temperature phases of (I) and (II) contains two pairs of independent molecules, where the molecules in each pair are related by noncrystallographic inversion centres. The molecules within each pair have the same absolute value of the inclination angle. The Flack parameter of the low-temperature phases is very close to 0.5, indicating inversion twinning. This can be envisaged as stacking faults in the low-temperature phases. It seems that competition between the primary amine-nitro N-H···O hydrogen bonds which form three-centred hydrogen bonds is the reason for the disorder of the nitro groups, as well as for the phase transition in both (I) and (II). The backbones of the structures are formed by N-H···N hydrogen bonding of moderate strength which results in the graph-set motif C(3). This graph-set motif forms a zigzag chain parallel to the monoclinic b axis and is maintained in both the high- and the low-temperature structures. The primary amine groups are pyramidal, with similar geometric values in all four determinations. The high-temperature phase of (II) has been described previously [Garden et al. (2004). Acta Cryst. C60, o328-o330].

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Section: Figure 16mentioning

confidence: 96%

Section: Figure 11mentioning

confidence: 99%

Section: Figure 11mentioning

confidence: 99%

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High- and low-temperature phases in isostructural 4-chloro-3-nitroaniline and 4-iodo-3-nitroaniline

et al. 2014

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“…Details of the relevant intensity measurements, structure refinement and data analysis for 1,3,4,6-tetra-Oacetyl-2-(trifluoromethylsulfonyl)-d-mannopyranose (Zhu & Jiang, 2007) (CSD refcode: UNEVAK01) are given in Flack & Bernardinelli (2008) …”

Section: Status Of Centrosymmetry and Resonant Scatteringmentioning

confidence: 99%

Analysing Friedel averages and differences

2012

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Various practical applications of the average (A) and difference (D) of Friedel opposites are described. Techniques based on the resonant‐scattering contribution to Friedel differences are applied to see whether a crystal is centrosymmetric or not, and to determine the point group of the crystal. For the validation of a structural study, plots of Aobs against Amodel, and Dobs against Dmodel are used extensively. Moreover, it is useful to display both plots on the same graph. Intensity measurements on a crystal of NaClO3 were made at three different speeds, with two different radiations and two different diffractometers, and treated with two different software packages and four different absorption corrections. The evaluation of these numerous data sets reveals underlying deficiencies. For comparison, plots of Aobs against Amodel, and Dobs against Dmodel are presented for two centrosymmetric crystals.

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“…Until date there have been several spectroscopic, diffraction methods developed to determine the absolute stereostructure of chiral molecules [26–35]. The non-empirical methods employed to determine the absolute configuration of a molecule include circular dichroism, exciton chirality methods [28–29], NMR spectroscopy [30–32], X-ray diffraction [33–35], etc.…”

Section: Introductionmentioning

confidence: 99%

Determination of the absolute stereostructure of a cyclic azobenzene from the crystal structure of the precursor containing a heavy element

Thomas¹,

Tamaoki²

2016

Beilstein J. Org. Chem.

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SummarySingle crystal X-ray diffraction has been used as one of the common methods for the unambiguous determination of the absolute stereostructure of chiral molecules. However, this method is limited to molecules containing heavy atoms or to molecules with the possibility of functionalization with heavy elements or chiral internal references. Herein, we report the determination of the absolute stereostructure of the enantiomers of molecule (E)-2, which lacks the possibility of functionalization, using a reverse method, i.e., defunctionalization of its precursor of known stereostructure with bromine substitution (S-(−)-(E)-1). A reductive debromination of S-(−)-(E)-1 results in formation of one of the enantiomers of (E)-2. Using a combination of HPLC and CD spectroscopy we could safely assign the stereostructure of one of the enantiomers of (E)-2, the reduced product R-(−)-(E)-1.

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Applications and properties of the Bijvoet intensity ratio

Cited by 32 publications

References 21 publications

High- and low-temperature phases in isostructural 4-chloro-3-nitroaniline and 4-iodo-3-nitroaniline

High- and low-temperature phases in isostructural 4-chloro-3-nitroaniline and 4-iodo-3-nitroaniline

Analysing Friedel averages and differences

Determination of the absolute stereostructure of a cyclic azobenzene from the crystal structure of the precursor containing a heavy element

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