Crossover Topology

It is very hard to analyze such an experiment if it does not produce a reporter strand, either directly, as described for the three-arm and four-arm junction, or after restriction frees it from catenated partners (Li et al. 1996). To characterize the flexibility of double-crossover molecules, it is useful to examine the crossover topology of the products of an oligomerization reaction. These are shown in Figure 17 for DAE, DAO and DAE+J motifs. It is clear that both DAE and DAE+J motifs produce a reporter strand, but DAO does not. Therefore, in our initial experiments, we have analyzed only DAE and DAE+J. In both, these motifs can be shown to behave as rigid species, because they do not cyclize to any appreciable extent. 

FIGURE 10.12 Typical potential energy surface topologies for spin crossover (a) and spin-forbidden addition of a ligand to a high-spin metal center (b). In many cases, AE is quite small.33... 

Finally the introduction of cyclopropane or vinylcyclopropane into organic compounds provides an opportunity to cross the odd/even manifolds in further synthetic steps aimed at the preparation of compounds of increased molecular complexity. Traditionally, any synthesis that involves intermediates with an odd number of atoms is more difficult because proper charge parity or consonance cannot be observed. A cyclopropane unit then functions as a topological operator in those cases where such crossover is desired. ... 

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