Displacement of groups

Metathesis of ethylene and butylenes to propylene. Another on-purpose route to propylene is metathesis, a chemical reaction that starts with two compounds, involves the displacement of groups from each and produces two new compounds. The application in this case converts ethylene and mixed butylenes to propylene and butene-1. This route could appeal to a company with refinery or olefins plant ethylene and butylenes that both have market values less than propylene, which could be the case in some local markets. 

D. Glycosylatiotts Involving Anometic Displacements of Groups other than Halides... 

The order of ease of displacement of groups from the phosphonium salts is allyl, benzyl > phenyl > methyl > 2-phenylethyl > ethyl, higher alkyls. The usefulness of this method for the preparation of various alkyldiphenylphosphine oxides from the available triphenylphosphine is particularly noteworthy. In contrast, the preparative value of this method is diminished in cases where the carbanions correspond ing to the leaving groups on the phosphorus have approximately the same stability. In some cases the reaction is used to prepare the carbon compound (equations 9 to 14). ... 

Figure 8.11 Plots of the work function versus the Mulliken electronegativities of the elements to illustrate the constant displacements of groups to determine P = EN-WF [43, 44],...

Imidazole reactivity was fully covered in CHEC-I, and only a brief summary is included here. The neutral molecule is Jt-excessive, being subject to electrophilic attack at N-3, less readily at C-4(5), and seldom at C-2. In benzimidazole electrophiles preferentially attack N-3 and the benzene ring carbons. Nucleophilic substitution reactions usually require some form of electron withdrawal elsewhere in the system, with displacements of groups at C-2 often favored. Imidazolium species are naturally more susceptible to nucleophilic attack, and they only undergo electrophilic substitutions with difficulty (e.g. nitration, sulfonation). The corresponding imidazole anions, when they can form, are highly reactive towards electrophiles. 

The compounds 9 and 10 prepared by the lithiation/substitution sequence from (1-dimethylaminoethyl)ferrocene, contain the dimethylamino group. They are useful as ligands themselves, but it was found that further modifications in the side chain lead to ligands 12-15 which are better suited for some purposes. The modifications make use of the retentive15-17 nucleophilic displacement of groups via ferrocene-stabilized carbocations and allow the introduction of many different substituents25-33. 

By contrast, the Lagrangian techniques attempt to describe the concentration statistics in terms of the statistical properties of the displacements of groups of particles released in the fluid. The mathematics of this approach is more tractable than that of the Eulerian... 

Two other possible segmental motions not depicted in Fig. 6 are in distinctly different time realms. At the slow end of the time scale (greater than milliseconds for reasonable amplitudes) are the Rouse-Zimm normal coordinate modes that result from the collective behavior of units of atoms (beads) along the chain pulling one another and acted on by Brownian forces, solvent frictional resistance, and other parts of the chain (Berne and Pecora, 1976). Librational motions, generally accorded to be of the order of 10 s , may also result from the thermally induced displacements of groups of atoms such wobbling motions have been proposed as important factors in the NMR relaxation of proteins (Howarth, 1979). 

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