 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 3]](wd5090fig3mag.jpg)
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Figure 3
AAS-induced symmetry breaking in p-bromobenzamide. The ORTEP plot in the upper part of the figure displays the packing of p-bromobenzamide molecules in the monoclinic crystal form viewed down the a axis. The glide plane is perpendicular to the b axis and the translational component is along c. Two p-bromobenzamide molecules which are related by the glide-plane symmetry operation are highlighted. The direction of linear polarization of the incident X-ray beam is also indicated for two experiments (I) and (II) that were carried out successively. In experiment (I), the C—Br bonds of the two symmetry-related molecules experience the polarization direction at different angles. Thus, in the vicinity of the Br K edge, these two Br atoms display different anomalous scattering factors and are no longer equivalent. This symmetry-breaking effect of AAS leads to the appearance of the glide-plane forbidden reflections [(h0l), l = odd] as is shown in the lower left part of the picture, which shows the reconstruction of the (h0l) layer from experimental data. In experiment (II), the direction of linear polarization of the incident X-ray beam was oriented parallel to the glide plane. The C—Br bonds of the two symmetry-related molecules therefore experienced the polarization direction at identical angles. Thus, in this particular configuration, the symmetry-equivalence of the two Br atoms is restored and the glide-plane forbidden reflections [(h0l), l = odd] are truly absent as is shown in the lower right part of the picture, which shows the reconstruction of the (h0l) layer from experimental data. |
![[Figure 3]](wd5090fig3.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
