Skeleton phase

The cross-sectional area of the solid phase perpendicular to the skeleton edge is calculated along all skeleton branches of the solid phase. The solid phase is then disconnected at the points corresponding to the absolute minima of that cross-sectional area for every skeleton edge (branch) cf. Grof et al. (2003). Examples of solid-phase fragments of the porous media formed by the disconnection of the solid-phase skeleton at weak points are shown in Figures 11 and 12. 

The structure-inherent higher total porosity (relatively wide channels between the smaller size structure of stationary phase skeleton) leads to a higher at given column size and thus to a higher solvent consumption. 

Infrared absorption properties of 2-aminothiazole were reported with those of 52 other thiazoles (113). N-Deuterated 2-aminothiazole and 2-amino-4-methylthiazo e were submitted to intensive infrared investigations. All the assignments were performed using gas-phase studies of the shape of the vibration-rotation bands, dichroism, isotopic substitution, and separation of frequencies related to H-bonded and free species (115). With its ten atoms, this compound has 24 fundamental vibrations 18 for the skeleton and 6 for NHo. For the skeleton (Cj symmetry) 13 in-plane vibrations of A symmetry (2v(- h, 26c-h- Irc-N- and 7o)r .cieu.J and... 

The most widely used particulate support is diatomaceous earth, which is composed of the silica skeletons of diatoms. These particles are quite porous, with surface areas of 0.5-7.5 m /g, which provides ample contact between the mobile phase and stationary phase. When hydrolyzed, the surface of a diatomaceous earth contains silanol groups (-SiOH), providing active sites that absorb solute molecules in gas-solid chromatography. 

Aluminum chloride [7446-70-0] is a useful catalyst in the reaction of aromatic amines with ethyleneknine (76). SoHd catalysts promote the reaction of ethyleneknine with ammonia in the gas phase to give ethylenediamine (77). Not only ammonia and amines, but also hydrazine [302-01-2] (78), hydrazoic acid [7782-79-8] (79—82), alkyl azidoformates (83), and acid amides, eg, sulfonamides (84) or 2,4-dioxopyrimidines (85), have been used as ring-opening reagents for ethyleneknine with nitrogen being the nucleophilic center (1). The 2-oxopiperazine skeleton has been synthesized from a-amino acid esters and ethyleneknine (86—89). 

Nowadays, almost all commercially available HPLC stationary phases are also applicable to planar chromatography. In addition to the polar hydroxyl groups present on the surface of native silica, other polar functional groups attached to the silica skeleton can also enter into adsorptive interactions with suitable sample molecules (34). Silica with hydrophilic polar ligands, such as amino, cyano, and diol functions, attached to the silica skeleton by alkyl chains, all of which have been well proven in HPLC, have also been developed for TLC (34). 

By covalently attaching reactive groups to a polyelectrolyte main chain the uncertainty as to the location of the associated reactive groups can be eliminated. The location at which the reactive groups experience the macromolecular environment critically controls the reaction rate. If a reactive group is covalently bonded to a macromolecular surface, its reactivity would be markedly influenced by interfacial effects at the boundary between the polymer skeleton and the water phase. Those effects may vary with such factors as local electrostatic potential, local polarity, local hydrophobicity, and local viscosity. The values of these local parameters should be different from those in the bulk phase. 

The reactivity modification or the reaction rate control of functional groups covalently bound to a polyelectrolyte is critically dependent on the strength of the electrostatic potential at the boundary between the polymer skeleton and the water phase ( molecular surface ). This dependence is due to the covalent bonding of the functional groups which fixes the reaction sites to the molecular surface of the polyelectrolyte. Thus, the surface potential of the polyion plays a decisive role in the quantitative interpretation of the reactivity modification on the molecular surface. 

The first microwave-assisted Suzuki reactions involving heteroaromatic skeletons were reported in 1996 [35]. Hallberg et al. Hnked the substrates 4-iodo and 4-bromobenzoic acid to a TentaGel-Rink resin (Scheme 16). Suzuki reactions on these soUd-phase-Unked substrates were easily performed in less than 4 min using a constant microwave irradiation power (45 W) (no temperature control Standard acidic cleavage with TEA yielded the corresponding biaryls with an excellent yield. 

Abstract An overview on the microwave-enhanced synthesis and decoration of the 2(lH)-pyrazinone system is presented. Scaffold decoration using microwave-enhanced transition-metal-catalyzed reactions for generating structural diversity, as well as the conversion of the 2(lH)-pyrazinone skeleton applying Diels-Alder reactions to generate novel heterocyclic moieties are discussed. The transfer of the solution phase to polymer-supported chemistry (SPOS) is also described in detail. 

In the crystal structure of these phases with tetragonal symmetry (P4/mbm, D h) the boron covalent sublattice is formed by chains of octahedra, developing along the c axis and by pairs of B atoms, bonding the octahedra in the xOy plane (see Fig. 1). The resulting three-dimensional skeleton contains tunnels parallel to the c axis that are filled by metal atoms . ... 

While it is possible to obtain a stoiehiometric Na,BogB,4 sodium boride when operating under Na pressure, the pyrolysis of the compound at low T and in high vacuum leads to Na,B(,gBi4 sodium-deficient phases where x can reach a value of 0 without the collapse of the boron skeleton". 

Solution The gas-phase volume, s,o,aiV, is the entire reactor except for the volume taken up by mechanical parts and by the skeleton of the catalyst... 

Eq. (128) affords apparently two interesting results (a) Since is always greater than zero, in the gas phase, equilibria (112) or (114) should always favor the radicals and (b) the larger the skeleton, the lower the value of Jmm thus, more extensive n radicals should disproportionate more easily. 

With the chemical structure of PbTX-1 finally known and coordinates for the molecule available from the dimethyl acetal structure, we wanted to return to the natural product crystal structure. From the similarities in unit cells, we assumed that the structures were nearly isomorphous. Structures that are isomorphous are crystallographically similar in all respects, except where they differ chemically. The difference between the derivative structure in space group C2 and the natural product structure in P2. (a subgroup of C2) was that the C-centering translational symmetry was obeyed by most, but not all atoms in the natural product crystal. We proceeded from the beginning with direct methods, using the known orientation of the PbTX-1 dimethyl acetal skeleton (assuming isomorphism) to estimate phase... 

Just as the Mo6Xg units in the Chevrel phases tolerate a certain lack of electrons (e.g. 20 instead of 24 skeleton electrons), clusters with M6X12 units which have fewer than 16 skeleton electrons are also possible. For example, in Zr6I12 there are only 12 skeleton electrons, and Sc7Cl12 = Sc3+[Sc6C112]3- has only nine. 

Minakuchi, H., Nakanishi, K., Soga, N., Ishizuka, N., Tanaka, N. (1997). Effect of skeleton size on the performance of octadecylsilylated continuous porous silica columns in reversed-phase liquid chromatography. J. Chromatogr. A 762, 135-146. 

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