Selectivity-functional group dependency

The many possibilities of directing the physical/chemical properties of a den-drimer by introduction of selected functional groups into the molecule lead to an great variety of potential applications of dendrimers. Depending upon the position and the nature of the functional units within the dendrimer structure, it is possible to distinguish between different types of functional dendrimers ... 

Despite the high cost of the equipment required and the time taken for sample preparation and spectra acquisition, MAS-HR NMR provides invaluable stmctural information about the species present in a reaction. Only a few milligrams of resin beads are required and they can be recovered as the technique is nondestructive. The complementarity of the technique with other analytical methods is clear MALDl-TOP cannot discriminate among compounds with the same MW and depends on the ionization properties of the resin-bound compound, while PTIR depends on the presence of selected functional groups in the molecule. MAS-HR NMR can be used independently from the nature of the performed reaction and the functional groups formed or lost during the SPS step. Additionally, two-dimensional MAS techniques such as 2D-COSY (correlated spectroscopy) and TOCSY (total correlated spectroscopy) (171) or 2D-SECSY (spin echo correlation spectroscopy) (181) can provide more detailed information that may be useful in specific cases. 

Melting points, boiling points, densities, and refractive indexes for carboxyUc acids vary widely depending on molecular weight, stmcture, and the presence of unsaturation or other functional groups (Tables 1,2,3, and 5). In addition, some useful constants for alkanoic acids are Hsted in Table 1. Some constants for selected unsaturated and substituted acids are given in Table 7. 

Since the stereochemical course of a catalytic hydrogenation is dependent on several factors, " an understanding of the mechanism of the reaction can help in the selection of optimal reaction conditions more reliably than mere copying of a published recipe . In the first section the factors which can influence the product stereochemistry will be discussed from a mechanistic viewpoint. In subsequent sections the hydrogenation of various functional groups in the steroid ring system will be considered. In these sections both mechanistic and empirical correlations will be utilized with the primary emphasis being placed on selective and stereospecific reactions. 

Nature of ion exchange resin. The absorption of ions will depend upon the nature of the functional groups in the resin. It will also depend upon the degree of cross-linking as the degree of cross-linking is increased, resins become more selective towards ions of different sizes (the volume of the ion is assumed to include the water of hydration) the ion with the smaller hydrated volume will usually be absorbed preferentially. 

Monomers employed in a polycondensation process in respect to its kinetics can be subdivided into two types. To the first of them belong monomers in which the reactivity of any functional group does not depend on whether or not the remaining groups of the monomer have reacted. Most aliphatic monomers meet this condition with the accuracy needed for practical purposes. On the other hand, aromatic monomers more often have dependent functional groups and, thus, pertain to the second type. Obviously, when selecting a kinetic model for the description of polycondensation of such monomers, the necessity arises to take account of the substitution effects whereas the polycondensation of the majority of monomers of the first type can be fairly described by the ideal kinetic model. The latter, due to its simplicity and experimental verification for many systems, is currently the most commonly accepted in macromolecular chemistry of polycondensation processes. 

Detectors are composed of a sensor and associated electronics. Design and performance of any detector depends heavily on the column and chromatographic system with which it is associated. Because of the complexity of many mixtures analysed and the limitation in regard to resolution, despite the use of high-resolution capillary columns and multicolumn systems, specific detectors are frequently necessary to gain selectivity and simplify the separation system. Many detectors have been developed with sensitivities toward specific elements or certain functional groups in molecules. Those detectors that exhibit the highest sensitivity are often very specific in response, e.g. the electron capture detector in GC or the fluorescence detector in LC. Because... 

On Pd/C, carbon-carbon double bonds and halogens are usually reduced before the N-oxides. The final selectivity in the hydrogenation of N-oxides has been shown to depend on the pH, the catalyst system used, and the functional groups present and their position. PtSx was a superior catalyst with a higher assay and yield in the selective hydrogenation of 6-chloro-2(lH)-hydroxyqui-noxaline-4-oxides (43) (Scheme 4.139).534... 

IR spectroscopy is a powerful and readily available orientation characterization technique. It offers a high chemical selectivity since most functional groups absorb at distinct wavelengths (typically in the 2.5-25 pm range (4,000 00 cm-1 range)), which often depend on their local environment. IR spectroscopy thus provides qualitative and quantitative information about the chemical nature of a sample, its structure, interactions, etc. The potential of IR spectroscopy for orientation characterization stems from the fact that absorption only occurs if the electric field vector of the incident radiation, E, has a component parallel to the transition dipole moment, M, of the absorbing entity. The absorbance, A, is given... 

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