reflections

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: