Cis/trans structure

If MoClj is used, a trans-polyalkaiamer is fonned when ReClj is the catalyst, the cis-polymer is produced and if the monomer is reacted in the presence of WClg, a mixed cis-trans structure is obtained. 

Schrock, R. R. Lee, J.-K. O Dell, R. Oskam, J. H. Exploring factors that determine cis/trans structure and tacticity in polymers prepared by ring-opening metathesis polymerization with initiators of the type syn- and anfi-Mo(NAr)(CHCMe2Ph)(OR)2. Observation of a temperature-dependent cis/trans ratio. Macromolecules 1995,28,5933-5940. 

Draw cis-trans structures of any of the following square planar or octahedral complexes that exhibit geometric isomerism. Label the drawings cis or trans. 

The utility of the least motion concepts is further illustrated by work on the solid-state synthesis of (SN)x from S2N2(23,24). Both the S2N2 phase and the final solid-state reaction product are monoclinic, with the same space group (P22 /c)and four SN units per unit cell(25-27). Consequently, since the polymer chains in (SN) are in the unique axis direction (b), it was initially believed that reaction occurred in the crystallographic direction in S2N2 The least motion calculations indicate that formation of an all trans chain requires much larger 6 than is required for formation of a cis-trans chain, which is in agreement with the observed cis-trans structure of (SN). More important, these calculations indicate that a much smaller 6 (0.488) is required for reaction in the a-axis direction than for reaction in the b-axis direction (1.208) or for any other possible reaction mode(23). 

FTIR-MALDI polymer and dendrimer characterisation and structure isotacticity, cyclo and oligolactides, polymerisation kinetics, molecular weight evaluations, diblock polymers-oligomer studies and cis-trans structures. 

Although molecular symmetry is well understood, until the development of proton nuclear magnetic resonance (NMR), and later C-NMR, a study of this aspect of polymer structure presented problems. A knowledge of short and long chain branching in polymers and other aspects of polymer structure such as stereochemistry, cis-trans structures and regioisomerism supplies not only information about the reaction kinetics, but also about the relationship between polymer chain structure and properties. 

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