Functional group placement

Molecular Length, Functional Group Placement, and Orientational Stability... 

Fig. 8.7. Surface imprinting with a covalently coupled diimine template has been used to position two amines onto a flat silica surface in an effort to isolate the effect of functional group placement in molecular imprinting. The rectangular spacer between the imines represents either a phenyl or diphenylmethane. Adapted from [37].

The Baldwin and Whitehead proposal [58] went on to suggest that the initial [4 + 2] adduct 119 can undergo redox exchange to give the pentacyclic intermediate 122 shown in Figure 3.6. Hydrolysis of the iminium ion functionality in 122 leads to a tetracyclic seco-skeleton containing an aldehyde functionality. The skeleton and aldehyde functionality present in the Baldwin and Whitehead tetracyclic intermediate 123 correspond exactly with the skeleton and aldehyde functional group placement in ircinals A (102) and B (103). Finally,... 

Biomacromolecules such as proteins derive their function from their three-dimensional shape and the precise functional group placement on the surface and interior of the structure. Also known as the tertiary structure, this shape is a result of a perfectly controlled monomer sequence, or primary structure. Synthetic polymers containing a perfect monomer sequence are inaccessible using contemporary techniques. However, recent advances in polymerization techniques allow for the fabrication of multi-block polymers with narrow molecular weight distributions " and materials with relatively controlled monomer sequences by step-growth and chain-growth... 

Amphiphilic homopolymers containing both hydrophilic (carboxylic acid units) and lipophilic (benzyl moieties) functionalities in each repeat unit have been reported to assembly [180]. These polymers are soluble in both aqueous and organic solvents, where they assemble into micelle-like or inverse miceUe-Uke structures. All these solutions were optically clear. The hydrophilic carboxyhc acid unit and the hydrophobic benzyl moiety are placed on the opposite sides of the polymer backbone in solvents of different polarity. The observed solubUity characterishcs are the result of formation of a micehe-like structure in water, in which the hydrophihc carboxylate groups are exposed to the bulk solvent and the hydrophobic benzyl substituents are tucked in the interior of an assembly (Scheme 7). Similarly, an inverted micelle-like structure would be expected in apolar solvents, in which the functional group placements are reversed. 

In recognition of the specificity of natural processes, much synthetic catalysis research is focused on developing new catalysts to control functional group placement, monomer sequence control, molecular architecture, and molecular weight in polymer synthesis. These catalysts may be considered natural mimics. 

Structural flexibility relative to functional groups and their placement. 

Functional groups can be introduced at different locations in the dendrimer. Placement in the core of the dendrimer results in a topological isolation and protection of the functional group from the environment [48,49]. Furthermore, single shells of the dendrimer corresponding to different generations can be endowed with functionalities [50]. Thus particles with functions having a defined depth under the surface can be realized. The decoration of the dendrimer sur-... 

Interactions can be combined by a designed placement of functional groups in the molecular skeleton to generate supramolecular synthons, which are defined as structural units within supermolecules that can be formed and/or assembled by known or conceivable synthetic operations involving intermolecular interactions (Desiraju, 1995). In other words supramolecular synthons are spatial arrangements of intermolecular interactions. 

In this paper detailed methods for the determination of placement and assay of silicon hydride (Si-H), silicon hydroxide (Si-OH) and silicon phenyl (Si-0) functional groups in molecular weight components of silicones of the Sylgard (Dow-Corning Co.) type will be described. The methods are illustrated with the analysis of Sylgard addition prepolymers and of model polydimethylsiloxanes (PDMS). 

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