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Geometry chiral

Bonnet LG, Douthwaite RE, Hodgson R. Synthesis of constrained-geometry chiral di-N-heterocyclic carbene ligands and their silver(I) and paUadium(II) complexes. [Pg.273]

Epitaxy of Isotactic Poly (1-butene) Isotactic poly(1-butene) (iPBul) is an archetypical polymorphic polymer with three different structures that differ by the chain conformation, and thus by the unit-cell geometry and symmetry (cf Chapter 2).The three crystal phases could be obtained by epitaxial crystallization on appropriate substrates [48-50]. Most interesting among them are the epitaxy of Form I (trigonal unit cell, threefold helical conformation, racemic phase) and that of Form III (orthorhombic unit cell, fourfold helical geometry, chiral crystal phase). [Pg.250]

If compounds have the same topology (constitution) but different topography (geometry), they are called stereoisomers. The configuration expresses the different positions of atoms around stereocenters, stereoaxes, and stereoplanes in 3D space, e.g., chiral structures (enantiomers, diastereomers, atropisomers, helicenes, etc.), or cisftrans (Z/E) configuration. If it is possible to interconvert stereoisomers by a rotation around a C-C single bond, they are called conformers. [Pg.75]

The stereochemical outcome of these reactions can be explained by considering the transition-state geometry. For example, applying the Houk model (495) to akyhc alcohols and their derivatives, the smallest substituent at the preexisting chiral center is oriented "inside" over the face of the transition-state ring and the oxygen atom "outside" (483). [Pg.322]

Woodward s total synthesis of cephalosporin C begins with L-cysteine (48) which establishes the chiral center at C-7. The cis geometry at C-6,7 is achieved in intermediate (49) which is cyclized to (50) by treatment with triethylaluminum. The dihydrothiazine ring is constructed by Michael addition to the condensation product of trichloroethyl glyoxylate... [Pg.294]

We have carried out a series of geometry optimizations on nanotubes with diameters less than 2 nm. We will present some results for a selected subset of the moderate band gap nanotubes, and then focus on results for an example chiral systems the chiral [9,2] nanotube with a diameter of 0.8 nm. This nanotube has been chosen because its diameter corresponds to those found in relatively large amounts by Iijima[7] after the synthesis of single-walled nanotubes. [Pg.43]

Verify, by making molecular models, that the bonds to sulfur are arranged in a trigonal pyramidal geometry in sulfoxides and in a tetrahedral geometry in sulfones. Is phenyl vinyl sulfoxide chiral What about phenyl vinyl sulfone ... [Pg.686]

Each of the following molecules might be resolved into two enantiomers if 1) the molecule s preferred geometry is chiral, and 2) the molecule s enantiomeric forms do not readily interconvert (this interconversion is called configuration inversion ). [Pg.71]

Examine the geometry of 3-methyl-3-hexyl bromide, and assign the configuration (R or S) to the chiral atom. Examine the geometry of 3-methyl-3-hexyl cation. Is it chiral ... [Pg.96]

The absolute configuration of products obtained in the highly stereoselective cycloaddition reactions with inverse electron-demand catalyzed by the t-Bu-BOX-Cu(II) complex can also be accounted for by a square-planar geometry at the cop-per(II) center. A square-planar intermediate is supported by the X-ray structure of the hydrolyzed enone bound to the chiral BOX-copper(II) catalyst, shown as 29b in Scheme 4.24. [Pg.181]

One consequence of tetrahedral geometry is that an amine with three different substituents on nitrogen is chiral, as we saw in Section 9.12. Unlike chiral carbon compounds, however, chiral amines can t usually be resolved because the two enantiomeric forms rapidly interconvert by a pyramidal inversion, much as an alkyl halide inverts in an Sfg2 reaction. Pyramidal inversion occurs by a momentary rehybridization of the nitrogen atom to planar, sp2 geometry, followed by rehybridization of the planar intermediate to tetrahedral, 5p3 geometry... [Pg.919]

In normal carbonium-ion chemistry, reaction proceeds from a precursor with a tetrahedral carbon capable of asymmetry hence, the stereochemistry of displacement in an aliphatic system can be ascertained by observation of the fate of the chiral center from reactant to product. An ethylenic system, of course, has no such chiral center, and hence there can be no change in optical configuration as the reaction proceeds. However, the stereochemistry of vinylic displacement and hence the symmetry and geometry of the intermediate can be... [Pg.276]

Chirality is an important part of today s chemistry and, in this respect, the pseudo-octahedral geometry of hexacoordinated phosphorus derivatives is interesting as it suffices to coordinate to the central atom three identical sym-... [Pg.21]


See other pages where Geometry chiral is mentioned: [Pg.220]    [Pg.1385]    [Pg.404]    [Pg.220]    [Pg.1385]    [Pg.404]    [Pg.1283]    [Pg.2450]    [Pg.419]    [Pg.196]    [Pg.490]    [Pg.490]    [Pg.91]    [Pg.735]    [Pg.201]    [Pg.262]    [Pg.32]    [Pg.55]    [Pg.60]    [Pg.110]    [Pg.158]    [Pg.108]    [Pg.71]    [Pg.139]    [Pg.170]    [Pg.268]    [Pg.258]    [Pg.27]    [Pg.142]    [Pg.134]    [Pg.294]    [Pg.164]    [Pg.164]    [Pg.168]    [Pg.133]    [Pg.207]    [Pg.121]    [Pg.135]    [Pg.111]    [Pg.20]    [Pg.127]   
See also in sourсe #XX -- [ Pg.219 , Pg.220 ]

See also in sourсe #XX -- [ Pg.219 , Pg.220 ]




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Distance geometry chiral constraints

Ligands chiral geometry

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