Thermodynamically determined

The lithium-(-)-sparteine complex, generated by deprotonation of 1-methylindene, does not lose its configuration in diethyl ether solution even at room temperature80 presumably, the observed major diastcreonier is the thermodynamically determined product. Substitution with carbonyl compounds leads to 1-substituted (fl)-l-methyl-l//-indenes with >95% ee in high yields81. 

We have considered volume changes resulting from density changes in liquid and gaseous systems. These volume changes were thermodynamically determined using an equation of state for the fluid that specifies volume or density as a function of composition, pressure, temperature, and any other state variable that may be important. This is the usual case in chemical engineering problems. In Example 2.10, the density depended only on the composition. In Example 2.11, the density depended on composition and pressure, but the pressure was specified. 

The Mg content of hydrothermally altered volcanic rocks is reflected by the extent of seawater-volcanic rock interaction at elevated temperatures, because it has been experimentally and thermodynamically determined that nearly all of the Mg in seawater transfer to volcanic rocks, owing to the reaction of the cycled seawater with volcanic rocks at elevated temperatures (Bischoff and Dickson, 1975 Mottl and Holland, 1978 Wolery, 1979 Hajash and Chandler, 1981 Reed, 1983 Seyfried, 1987). It has been shown that the CaO content of hydrothermally altered midoceanic ridge basalt is inversely correlated with the MgO content with a slope of approximately — 1 on a molar basis (Mottl, 1983). This indicates that Ca of basalt is removed to seawater and Mg is taken up from seawater by the formation of chlorite and smectite during the seawater-basalt interaction. This type of reaction is simply written as ... 

Because the acid dissociation constants in solution are generally known, and also, often the solvation energies of the neutral AH have been determined by neutral gas-phase solution equilibria, equation 8 can be used to obtain the sum of the solvation energies AG°ol(A-) + AG°ol (H30+). When this approach is applied to a series of acids AH, values for the solvation energies AG°ol (A-), relative to the constant AG, (H30+), can be obtained. Such thermodynamic determinations of the... 

The Langmuir film balance experiment as described above is generally considered to be thermodynamically determined by the relation between the independent variables temperature, surface pressure, and molecular area. 

The following expression is stringent thermodynamical determination of the osmotic pressure... 

Chemists use both thermodynamics and rate to study chemicai reactions. Thermodynamics determines whether a reaction wiii occur at a certain temperature and when equiiibrium wiii be reached. The rate of a reaction determines the time it takes for a certain concentration of product to form. In this section, you wiii iearn about the extent of a reaction the reiative concentrations of products to reactants at equiiibrium. 

Usually, the enantiomeric ratios decrease on prolonged reaction times to approach the thermodynamically determined ratios of diastereomers. Notable exceptions are the lithium-)—)-sparteine derivatives of (2-methyl-l-cycloalkenyl)methyl carbamates ewf-303d... 

In 1972, Christian Anfinsen received the Nobei Prize in Chemistry for his principie of thermodynamic determinism, that the amino acid sequence aione determines the three-dimensionai structure. In the normal physiological state, the three-dimensional structure of a protein is the one in which the Gibbs free energy of the whole system is at a minimum. Many protein molecules have segments that are folded into a single-stranded a-helix, which is held together by the hydrogen bonds between coils, called a secondary structure. 

The preceding section discussed how the chemist can make a thermodynamic determination of the spontaneity of a chemical reaction. However, even if these calculations indicate that a reaction should be quite spontaneous (the value for oG is a large, negative number), there is no guarantee that the reaction will proceed rapidly... 

Of course, self-assembly of this kind occurs in water, and not, say, in ethanol. Any self-organization process must be defined in a given set of initial conditions. Initial conditions, as always in thermodynamics, determine the outcome of the process, and in particular whether the process is also under thermodynamic control or not. Aside from that, it is well known that a large series of amphiphilic molecules... 

Before we proceed, however, it is important to review briefly the roles thermodynamic and kinetic considerations play in determining the structure. In some cases, the distinction is easy to establish. In the case of the association colloids we discussed in Chapter 8, thermodynamics determined the formation and the structure of the colloidal particles and their subsequent transformations to more complex structures at higher concentrations of the particles. In... 

The second law of thermodynamics determines how much work can be extracted from a process for maximum work output there is an associated minimum heat output ... 

We say that thermodynamics determines whether a process could occur, because thermodynamics tells us only whether the process is possible, not whether it actually does occur in a finite period of time. The rate at which a thermodynamically possible reaction occurs depends on the detailed mechanism of the process. For a biochemical pro-... 

Thermodynamics (determining the fundamental parameters on which the process can be analysed). 

It is interesting to note that the cis-trans ratios obtained by Ghorbel and coworkers (312) on 1-butene isomerization were mostly unaffected by the chemisorption of the different poisons and corresponded to the thermodynamically determined ratio. The same result was obtained by Knozinger and Aounallah (377), when 1-butene was isomerized in a recirculating reactor at 120°C on tj-A1203 (activated at 500°C) that was partially poisoned by pyridine. In micro-catalytic pulse experiments, on the other hand, one observes kinetically determined primary product distributions with cis-trans ratios of about 2 (370). Different types of active sites appear, therefore, to be involved in the doublebond shift and in the cis-trans isomerization, the latter remaining unaffected by pyridine chemisorption. 

Semisolid Casting Fundamentally, a semisolid material is a mixture of liquid and solid phases. In metal alloys, thermodynamics determine the temperatures at which solid, liquid, or both exist. This is usually represented by a phase diagram, which maps phases present as a function of temperature and composition. For most alloy compositions, there is a freezing range where both liquid... 

Additionally, the rate of heat transfer may also become important. Nonuniform temperature distributions within the solid particles result in differing local rates of reaction, as the reaction rates are strongly depending on the temperature according to the Arrhenius law. Heat- and mass-transfer effects become increasingly important with increasing rates of reaction [1]. Whereas the macroscopic kinetics describe the rate of a chemical reaction, thermodynamics determines the maximum extent to which reactions can occur. Provided that the rate of reaction is sufficiently fast, the thermodynamical equilibrium can be reached. 

Thermodynamics determines the possibility, kinetics the actuality of the conversion. 

Thermodynamic Control at 40 °C At 40 °C, a significant fraction of molecular collisions have enough energy for reverse reactions to occur. Notice that the activation energy for the reverse of the 1,2-addition is less than that for the reverse of the 1,4-addition. Although the 1,2-product is still formed faster, it also reverts to the allylic cation faster than the 1,4-product does. At 40 °C, an equilibrium is set up, and the relative energy of each species determines its concentration. The 1,4-product is the most stable species, and it predominates. Since thermodynamics determine the results, this situation is called thermodynamic control (or equilibrium control) of the reaction. The 1,4-product, favored under these conditions, is called the thermodynamic product. 

Thermodynamics determines whether or not a monomer will polymerize, to what extent it polymerizes, and what conditions such as solvent, temperature, and concentrations are required. As discussed in Chapter 1, the thermodynamic polymerizability of a monomer is independent of the mechanism and is therefore identical for radical, anionic, cationic, and coordinative mechanisms if structurally identical polymers are obtained. Although this requires that both the end groups and the microstructure are the same, the influence of regioselectivity and stereoselectivity on the enthalpy and/or entropy of polymerization has not been confirmed experimentally yet. 

Kurihara-Beigstrom, T., Flynn, G. L. and Higuchi, W. I. Physicochemical study of percutaneous absorption enhancement by dimethyl sulfoxide Kinetic and thermodynamic determinants of dimethyl sulfoxide mediated mass transfer of alkanols. Journal of Pharmaceutical Sciences 75(5) 479-486, 1986. 

The main characteristics of the green mixture used to control the CS process include mean reactant particle sizes, size distribution of the reactant particles reactant stoichiometry, j, initial density, po size of the sample, D initial temperature, Tq dilution, b, that is, fraction of the inert diluent in the initial mixture and reactant or inert gas pressure, p. In general, the combustion front propagation velocity, U, and the temperature-time profile of the synthesis process, T(t), depend on all of these parameters. The most commonly used characteristic of the temperature history is the maximum combustion temperature, T -In the case of negligible heat losses and complete conversion of reactants, this temperature equals the thermodynamically determined adiabatic temperature (see also Section V,A). However, heat losses can be significant and the reaction may be incomplete. In these cases, the maximum combustion temperature also depends on the experimental parameters noted earlier. 

In the polymerization of dialkyldichlorosilanes with sodium in refluxing toluene, propagation and a concurrent back-biting reaction to cyclic material could give the range of products found if the products are kinetically, instead of thermodynamically, determined (12). No evidence for depolymerization has been found for the reaction in toluene solution. 

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