Two-dimensional connectivity

Table 2-10 is a two-dimensional connectivity table for the hydrogen-.suppressed phenylalanine molecule. No three-dimensional representation i.s implied. Further, this type of connectivity table will be the. same for molecules with asymmetric atoms (D versus 1.) or for those that can exist in more than one conlbrmaliun (i.c.. "chair versus "boat conformation. ami versus Kmichc versus eclipsed). 

As indicated above, Si MAS NMR can provide a wealth of structural information on zeolites, limited in the case of highly siliceous samples only by the spectral resolution. In solution, the application of two-dimensional NMR techniques has provided considerable information on the two-dimensional connectivities between atoms within molecular structures [63]. For example, the HSC (heteronuclear shift correlation) sequence establishes heteronuclear connections such as Si/ H, etc. the COSY sequence defines homonuclear correla-... 

The reliability of these two-dimensional connectivity experiments is now well enough established that they can be used with confidence in the investigation of unknown structures in conjunction with diffraction studies. In a first step in this direction, a study of the three-dimensional bonding connectivities in ZSM-11 in both its high- and low-temperature forms has been reported [86]. As described earlier these are related to each other by a temperature-induced phase transition. The high-temperature form is known to have tetragonal symmetry with space... 

Figure 3.10 Proposed Ge allotropes based on Ceg building units, (a) Two-dimensional connection of nido-Ceg clusters forming a LPesU sheet [88] (b) OCesJJ nanotube...

Connectivity of the pore space is important in applications. One-dimensional connectivity refers to access of a molecule being restricted to a single channel the many examples include low silica zeolites such as zeolite L and high silica zeolites such as SSZ-24. Two-dimensional connectivity requires a molecule to have access to any part of a planar dimensional arrangement of pore space... 

Since DNA can be involved in multiple junctions (Chapter 10.4), it should be employable as a nanoscale constructional material. High two-dimensional connectivity, for example, enables six-point star structures to be assembled [103] (Figure 11.50a). Various three-dimensional structures can also be built up as, for example. Figure 11.50b. Self-assembled bipyramids as well as DNA with 8 and 12 junctions have been reported [104,105], Nanotubes and cavity structures have been synthesised as well as DNA micelles [108], DNA molecular sieves and so forth [106-108]. 

Procter et al. have followed up with the first reported two-dimensional connective Pummerer cyclisation. A mixture of regioisomeric > -oxindoles is formed, with the the linear regioisomer being the more prevalent. Each regioisomer was a 1 1 mixture of diastereoisomers. Yields were reported over the two steps as the glyoxamides were not purified. As before, the sulphides were cleaved with Sml2. 

Both 3-2 and 3-1 composites have a three-dimensionally connected ceramic phase. The second (polymer) phase is one- or two-dimensionally connected within the ceramic network. This tends to produce extremely rugged composites. 

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