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Topological diastereomers

Ctt(I) complexes by KCN led to the corresponding free ligands represented in Fig. 33. Demetallation of 852+ afforded the free trefoil knot 86 as a colourless glass. Very small amounts (0.5%) of 87, the unraveled topological diastereomer of 86 could also be isolated and characterized. [Pg.155]

The structures XI to XIII or XIV and XV are topological stereoisomers since they have identical connectivity (homeomorphic), but no continuous deformation will allow them to interconvert (not isotopic). Furthermore, structures XII and XIII are topological enantiomers and the knots XII or XIII and the unknotted ring XI are topological diastereomers. [Pg.180]

Fig. 1 Constitutional isomers, topological isomers, topological diastereomer.s. and topological enantiomers. (View this art in color at www.deklcer.com.)... Fig. 1 Constitutional isomers, topological isomers, topological diastereomer.s. and topological enantiomers. (View this art in color at www.deklcer.com.)...
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]

Singly and doubly interlocked [2]catenanes can exist as topological stereoisomers (see p. 144 for a discussion of diastereomers). Catenanes 35 and 36 are such stereoisomers and would be expected to have identical mass spectra. Analysis showed that 35 is more constrained and cannot readily accommodate an excess of energy during the mass spectrometry ionization process and, hence, breaks more easily. [Pg.114]

The properties given so far can be summarized thus that constitutional isomers differ in topologic properties diastereomers differ in geometric properties and that... [Pg.3]

Whatever the beauty of the resolved systems discussed above, it should be noticed that the enantiomers obtained after resolution are not topological enantiomers but classical geometrical diastereomers. In each case, a rigid chiral function... [Pg.135]

A further shortcoming of the most commonly used topological indices is the inability to take into account stereo-specific properties of molecules, such as atomic chiralities, enantiomers (R-and S-isomers), and - and I J-diastereomers (Z- and E-isomers). Topological descriptors proposed to fill the gap to account for chirality and ZE-isomerism can be found in Schultz et al. (1995), de Julian-Ortiz et al. (1998), and Golbraikh et al. (2001) as well as in Lekishvili (1997 2001), and Golbraikh et al., (2002), respectively. It is probably a question of availability and time until the power of these descriptors is demonstrated and they begin to be used routinely in QSPR analysis. [Pg.90]

Fig. 15. Two consecutive counterclockwise (CCW) Ray-Dutt twists applied schematically to a model complex like 30-32. While each of the two processes exchanges diastereomers, the combined action is topologically equivalent to an (0,0)-1,2 shift. The eye drawn near one of the structures shows which triangular face was selected for the second twist process.45... Fig. 15. Two consecutive counterclockwise (CCW) Ray-Dutt twists applied schematically to a model complex like 30-32. While each of the two processes exchanges diastereomers, the combined action is topologically equivalent to an (0,0)-1,2 shift. The eye drawn near one of the structures shows which triangular face was selected for the second twist process.45...
Liquid extraction was used to make diastereomers, exploiting the high solubility of potassium triflate in water compared with the binaphthylphosphate salts. The two diastereomers have different solubilities and the (+) isomers of knot and anion crystallise together [49, 50], while the laevorotatory knot remains soluble. Counterion exchange with hexafluorophosphate gave the pure topological enantiomers. The optical rotatory power of the copper knots is very high At the sodium D-line (589 nm), the optical rotatory power was 7.000 mol 1 L dm They are beautiful molecules with a remarkable property ... [Pg.123]

The second major category of isomers and the focus of this chapter are stereoisomers. Being isomers they too have the same number and kind of building block atoms, but, unlike constitutional isomers, they have identical topologies. Stereoisomers, in turn, are divided into two groups enantiomers and diastereomers. Enantiomers are isomers that are not superimposable on their mirror images. And, by definition, diastereomers are all other stereoisomers that are not enantiomers. [Pg.330]

It is imperative to examine the effect of carcinogen-DNA adducts on the topology as well as conformation of DNA, since these properties are believed to influence the specific DNA interactions. From the spectroscopic studies (uv, CD, LD) it can be inferred that both B and Z forms of polynucleotides can covalently react with BaPDE with a very low affinity for the Z form [124, 127-128]. In fact, both diastereomers favour and preserve B-like conformations around the adduct site even at 4.5M NaCl. This might introduce flexibility in the poly (dG-dC). poly (dG-dC) structure manifested by a reduced LD signal [129]. Thus anri-BaPDE adduct formation may affect the behaviour of DNA selectively not only at the... [Pg.466]

The three-dimensional Wiener number (3-W) was introduced by Trinajstic and his co-workers and is based on the topographic (geometric) distance matrix. Thus, one can encode information on geometric diastereomers and conformers. The original Wiener number (two-dimensional Wiener index, denoted by Wor 2-lT) " was based on the distance matrix whose entries are topological distances between nonhydrogen atoms (2-Dij) and is the half-sum of all of these entries ... [Pg.4]

It is noteworthy that high quality QSARs cannot be developed if the critical factors related to bio activity are not present in the set of descriptors chosen. This is well illustrated with the activity of diastereoisomeric insect repellents. These molecules differ only in the spatial configuration of atoms. All topological, geometrical, and quantum chemical indices will have identical (redundant) values for the various diastereomers corresponding to the same empirical formula. Such situations call for novel approaches. As evident from our results on hierarchical overlay, the comparison of good quality structures generated by quantum chemical methods is needed in such cases. [Pg.76]

How are these stereoisomers different from conventional diastereomers The circle and the knot can be infinitely deformed— bent, twisted, stretched, and compressed— but they will never be interconverted (as long as we don t cross any bonds). Conventional isomers can be interconverted by deformation, as in the case of 2-butanol in Figure 6.9. Conventional stereoisomerism depends on the precise location of the atoms in space, leading to the terms geometric or Euclidian isomerism. With topological stereoisomers, we can move the atoms all around, and retain our isomerism. [Pg.325]

For each case in Figure 6.14, we have stereoisomers—structures with the same connectivities but differing arrangements of the atoms in space. They are not enantiomers, so they must be diastereomers. The novelty lies in the fact that these stereoisomers interconvert by a translation or reorientation of one component relative to the other. In some ways these structures resemble conformers or atropisomers, which involve stereoisomers that interconvert by rotation about a bond. For the supramolecular stereoisomers, however, interconversion involves rotation or translation of an entire molecular unit, rather than rotation around a bond. Note that for none of the situations of Figure 6.14 do we have topological stereoisomers. In each case we can interconvert stereoisomers without breaking and reforming bonds. [Pg.328]


See other pages where Topological diastereomers is mentioned: [Pg.140]    [Pg.229]    [Pg.325]    [Pg.326]    [Pg.329]    [Pg.140]    [Pg.229]    [Pg.325]    [Pg.326]    [Pg.329]    [Pg.75]    [Pg.493]    [Pg.202]    [Pg.21]    [Pg.192]    [Pg.203]    [Pg.55]    [Pg.88]    [Pg.22]    [Pg.167]    [Pg.1029]    [Pg.150]    [Pg.152]    [Pg.134]    [Pg.11]    [Pg.44]    [Pg.217]    [Pg.229]    [Pg.123]    [Pg.39]    [Pg.719]    [Pg.89]    [Pg.137]    [Pg.1620]    [Pg.1631]    [Pg.75]    [Pg.61]   
See also in sourсe #XX -- [ Pg.325 , Pg.329 ]




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