Aggregation of molecules

The catalysed reaction was considered to arise from the heterolysis of dinitrogen pentoxide induced by aggregates of molecules of nitric acid, to yield nitronium ions and nitrate ions. The reaction is autocatalytic because water produced in the nitration reacts with the pentoxide to form nitric acid. This explanation of the mechanism is supported by the fact that carbon tetrachloride is not a polar solvent, and in it molecules of nitric acid may form clusters rather than be solvated by the solvent ( 2.2). The observation that increasing the temperature, which will tend to break up the clusters, diminishes the importance of the catalysed reaction relative to that of the uncatalysed one is also consistent with this explanation. The effect of temperature is reminiscent of the corresponding effect on nitration in solutions of nitric acid in carbon tetrachloride ( 3.2) in which, for the same reason, an increase in the temperature decreases the rate. 

Dispersion The movement of aggregates of molecules under the influence of a gradient of concentration, temperature, and so on. The effect is represented hy Tick s law with a dispersion coefficient substituted for molecular diffusivity. Thus, rate of transfer = —Dj3C/3p). 

Segregated flow Occurs when all molecules that enter together also leave together. A state of aggregation is associated with every RTD. Each aggregate of molecules reacts independently of every other aggregate thus, as an individual batch reactor. 

Molecular solids are aggregates of molecules bound together by intermolecular forces. Substances that are gases under normal conditions form molecular solids when they condense at low temperature. Many larger molecules have sufficient dispersion forces to exist as solids at room temperature. One example is naphthalene (Cio Hg), a white solid that melts at 80 °C. Naphthalene has a planar structure like that of benzene (see Section 10-), with a cloud of ten delocalized n electrons that lie above and below the molecular plane. Naphthalene molecules are held in the solid state by strong dispersion forces among these highly polarizable n electrons. The molecules in... 

Our first investigations of the stereospecific aggregation of molecules in a monolayer involved the use of a novel chiral surfactant, AT-(a-methylbenzyl)stearamide, spread on aqueous acid subphases (Arnett and Thompson, 1981 Arnett et al, 1982). This surfactant was chosen for study because of the potential for strong hydrogen bonding between enantiomers, which should in theory yield closely packed aggregates in a film system. 

Micellar electrokinetic capillary chromatography (MEKC or MECC) is a more versatile technique than CZE due to its ability to separate neutral as well as ionic species. The term chromatography is used because a surfactant added to the buffer solution forms spherical aggregates of molecules... 

In order to achieve this, we should in principle calculate the energy of a given aggregate of atoms as a function of their positions in space. The results can be expressed as a many dimensional potential surface, the minima in which correspond to stable molecules, or aggregates of molecules, while the cols separating the minima correspond to the transition states for reactions leading to their interconveision. If such calculations could be carried out with sufficient accuracy, one could not only... 

In support of the association theory, colloid chemists cited non-reproduceable cryoscopic molecular weight determinations (which were eventually shown to be caused by errors in technique) and claimed that the ordinary laws of chemistry were not applicable to matter in the colloid state. The latter claim was based, not completely without merit, on the ascerta-tion that the colloid particles are large aggregates of molecules, and thus not accessible to chemical reactants. After all many natural colloids were shown to form double electrical layers and adsorb ions, thus they were "autoregulative" by action of their "surface field" (29). Furthermore, colloidal solutions were known to have abnormally high solution viscosities and abnormally low osmotic pressures. 

When the material is composed of an aggregation of molecules, one speaks of macroscopic polarization P, and for weak applied fields this is linearly dependent on the susceptibility % of the material in question, according to the relationship P = x E-... 

The ultimate goal of this work is to elucidate the contribution of shape and symmetry to the aggregation of molecules and ions. As... 

Molecular crystals are loosely bound aggregates of molecules which possess a large amount of internal stability, such as crystals of highly stable organic molecules. Since the constituent molecules are almost completely saturated, crystals of this type usually exert little catalytic activity they do not interact strongly with adsorbed molecules. 

The concept of micro- and macrofluids is of particular importance in heterogeneous systems because one of the two phases of such systems usually approximates a macrofluid. For example, the solid phase of fluid-solid systems can be treated exactly as a macrofluid because each particle of solid is a distinct aggregate of molecules. For such systems, then, Eq. 2 with the appropriate kinetic expression is the starting point for design. 

This aggregation of molecules is more likely to occur at low kinetic energies and at high densities of molecules. Thus, the value of R is affected by the reciprocals of temperature and molar volume. Beattie and Bridgeman proposed replacement of R by R(1 — c/VMT3). The form of the equation is based on theory the exponent of three on temperature is empirical. 

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