reflections

(noun)

Diffraction of X-rays by the layers of atoms within a crystal produces spots, or reflections recorded by a detector. The presence and intensity of reflections is the raw data of an X-ray crystallographic experiment.

Related Terms

  • goniometer
  • x-ray diffraction
  • x-ray crystallography

Examples of reflections in the following topics:

  • Chirality and Symmetry

    • Another way of describing a point of symmetry is to note that any point in the object is reproduced by reflection through the center onto the other side.
    • A plane of symmetry divides the object in such a way that the points on one side of the plane are equivalent to the points on the other side by reflection through the plane.
    • The existence of a reflective symmetry element (a point or plane of symmetry) is sufficient to assure that the object having that element is achiral.
    • Chiral objects, therefore, do not have any reflective symmetry elements, but may have rotational symmetry axes, since these elements do not require reflection to operate.
    • (i) Dissymmetry: The absence of reflective symmetry elements.
  • Determining Atomic Structures by X-Ray Crystallography

    • The x-ray beams are diffracted in a characteristic pattern that gives rise to reflections, dark spots on the detector which represent places where constructive interference of the diffracted light has occurred.
    • The detector records the reflections on a two-dimensional surface.
    • Then mathematical algorithms are applied in order to decode the information contained within the recorded reflections.
    • The two dimensional reflection pattern can be used to determine the atomic structure of the protein.
  • The Favorskii Rearrangement

    • Here the unsymmetrical cyclopropanone opens to favor the less substituted α-carbon, reflecting the carbanion stability order: 1º > 2º > 3º .
    • In this case cleavage of the cyclopropanol at the more substituted α-carbon probably reflects the inductive effect of the THPO substituent.
  • Addition to Carbonyl Double Bonds

    • Selective reduction of 4-tert-butylcyclohexanone (I) to a 10:1 mixture of trans- and cis-4-tert-butylcyclohexanol by LiAlH4 is an example of diastereoselectivity, reflecting a preference for hydride attack at the more hindered axial face of the carbonyl group.
    • The hindrance is reversed in compound III, and the products from LiAlH4 reduction reflect this difference.
  • Properties of Quartz and Glass

    • The individual crystallites may be transparent, but their facets (grain boundaries) reflect or scatter light, resulting in diffuse reflection.
    • Glass has the ability to refract, reflect, and transmit light according to the principles of geometrical optics.
    • According to the Fresnel equations, the reflectivity (the amount of light that gets reflected off the air-glass interface) of a sheet of glass is about 4% per surface (at normal incidence in air).
  • Fatty Acids

    • These long-chain carboxylic acids are generally referred to by their common names, which in most cases reflect their sources.
    • The higher melting points of the saturated fatty acids reflect the uniform rod-like shape of their molecules.
  • The Aldol Reaction

    • As a general rule for reactions involving cyclic transition states, E-enolates produce anti-aldols, and Z-enolates the syn-diastereomer, a tendency that reflects the facial selectivities of the transition states.
    • Enolborinates were among the most reliable and selective reagents revealed by a host of aldol studies, a quality reflected in reactions of the crotylboronates.
  • Bonding in Metals: The Electron Sea Model

    • Light cannot penetrate their surface; the photons simply reflect off the metal surface.
    • However, there is an upper limit to the frequency of light at which the photons are reflected.
  • By Functional Group

    • Consequently, apparent similarities may fail to reflect important differences.
  • Alkenes & Alkynes

    • The molecular formulas of these unsaturated hydrocarbons reflect the multiple bonding of the functional groups:
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