pyramidalization

(noun)

The conversion of a molecule's trigonal planar geometry to a tetrahedral one.

Related Terms

  • halogenation
  • halide

Examples of pyramidalization in the following topics:

  • The Configuration of Free Radicals

    • Since the difference in energy between a planar radical and a rapidly inverting pyramidal radical is small, radicals generated at chiral centers generally lead to racemic products.
    • However, unlike carbocation intermediates, which prefer to be planar, radicals tolerate being restricted to a pyramidal configuration.
    • Initial formation of a carboxyl radical is followed by loss of carbon dioxide to give a pyramidal bridgehead radical.
    • Although this is a 3º-alkyl halide, it does not undergo SN1 solvolysis reactions because of the strain imposed on the carbocation intermediate by its pyramidal confinement.
  • Stereogenic Nitrogen

    • As noted earlier, single-bonded nitrogen is pyramidal in shape, with the non-bonding electron pair pointing to the unoccupied corner of a tetrahedral region.
    • However, pyramidal nitrogen is normally not configurationally stable.
  • The Shape of Molecules

    • Of course, it is the configuration of atoms (not electrons) that defines the the shape of a molecule, and in this sense ammonia is said to be pyramidal (not tetrahedral).
    • For purposes of discussion we shall consider three other configurations for CH4, square-planar, square-pyramidal and triangular-pyramidal.
    • Since the tetrahedral, square-planar and square-pyramidal configurations have structurally equivalent hydrogen atoms, they would each give a single substitution product.
    • However, in the trigonal-pyramidal configuration one hydrogen (the apex) is structurally different from the other three (the pyramid base).
  • Reactive Intermediates

    • Carbanions are pyramidal in shape (tetrahedral if the electron pair is viewed as a substituent), but these species invert rapidly at room temperature, passing through a higher energy planar form in which the electron pair occupies a p-orbital.
    • Radicals are intermediate in configuration, the energy difference between pyramidal and planar forms being very small.
  • Nomenclature and Structure of Amines

    • In contrast, atropine, coniine, morphine, nicotine and quinine have stereogenic pyramidal nitrogen atoms in their structural formulas (think of the non-bonding electron pair as a fourth substituent on a sp3 hybridized nitrogen).
    • The other stereogenic nitrogens are free to assume two pyramidal configurations, but these are in rapid equilibrium so that distinct stereoisomers reflecting these sites cannot be easily isolated.
    • It should be noted that structural factors may serve to permit the resolution of pyramidal chiral amines.
    • An increase in angle strain in the sp2-hybridized planar transition state is responsible for the greater stability of the pyramidal configuration.
  • Lone Electron Pairs

    • The lone pair orbital will point toward the fourth corner of the tetrahedron, but since that position will be vacant, the NH3 molecule itself cannot be tetrahedral; instead, it assumes a pyramidal shape, more specifically, that of a trigonal pyramid (a pyramid with a triangular base).
  • Applying the VSEPR Model

    • Molecules with a coordination number of 5 are in the shape of a trigonal bipyramid; this consists of two triangular-based pyramids joined base-to-base.
    • In an AX6 molecule, six electron pairs will try to point toward the corners of an octahedron (two square-based pyramids joined base-to-base).
    • Here are the shapes that we will talk about: tetrahedral, trigonal pyramidal, bent, trigonal planar, linear.
  • Four-Membered Rings

    • Such electron pair delocalization is diminished in the penicillins, leaving the nitrogen with a pyramidal configuration and the carbonyl function more reactive toward nucleophiles.
  • Trihalides: Boron-Halogen Compounds

    • This trend is commonly attributed to the degree of π-bonding in the planar boron trihalide that would be lost upon pyramidalization (the conversion of the trigonal planar geometry to a tetrahedral one) of the BX3 molecule, which follows this trend: BF3 > BCl3 > BBr3 (that is, BBr3 is the most easily pyramidalized).
  • Oxidation States of Sulfur Compounds

    • Sulfoxides have a fixed pyramidal shape (the sulfur non-bonding electron pair occupies one corner of a tetrahedron with sulfur at the center).
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