Thermodynamic pathways

The final class of polymers containing carboranyl units to be mentioned here is the polyphosphazenes. These polymers comprise a backbone of alternating phosphorous and nitrogen atoms with a high degree of torsional mobility that accounts for their low glass-transition temperatures (-60°C to -80°C). The introduction of phenyl-carboranyl units into a polyphosphazene polymer results in a substantial improvement in their overall thermal stability. This is believed to be due to the steric hindrance offered by the phenyl-carborane functionality that inhibits coil formation, thereby retarding the preferred thermodynamic pathway of cyclic compound formation (see scheme 12). 

Thermodynamic Pathways and Electrostatic Free Energy Components The PBFE Method... 

When X is O, the endo-mode becomes the kinetic and the thermodynamic pathway. The resulting metallacarbe-noid is then ideally suited for a 1,2-hydride shift 353, which installs an endocyclic double bond. 

Of course, the reaction coordinate diagram might be such that kinetic and thermodynamic products are the same, e.g., pathway B would be both the kinetic and thermodynamic pathway, and its product would be both the kinetic and thermodynamic product. 

Although Curran s rate data for the reduction of radicals to organosamar-iums allow for an element of predictablity,2 problems can arise when multifunctional substrates are involved. For example, in the attempted intramolecular Barbier reaction of alkyl iodide 13, treatment with Sml2 results in the formation of side product 15 in addition to the expected product cyclohexanol 14 (Scheme 3.7).8 In this case, the p-keto amide motif in 13 is reduced at a rate competitive with alkyl iodide reduction, indicating that there are likely two mechanistic pathways through which the reaction proceeds a thermodynamic pathway initiated by reduction of the R I bond providing the... 

Chen, Y.-G. and Weeks, J. D., Different thermodynamic pathways to the solvation free energy of a spherical cavity in a hard sphere fluid. /. Chem. Phys. 118, 7944-7953... 

Provide a mechanism for the following reaction. Draw a reaction energy coordinate diagram that illustrates the kinetic and thermodynamic pathways for this reaction. 

When toluene is sulfonated (concentrated H2SO4) at room tempreratme, predominantly (about 95% of the total) ortho and para substitution occurs. If elevated temperatures (150-200 °C) and longer reaction times are employed, meta (chiefly) and para substitution account for some 95% of the products. Account for these differences in terms of kinetic and thermodynamic pathways. (Hint OT-Toluenesulfonic acid is the most stable isomer.)... 

Thermodynamic pathways reflect programs that direct a system from one state to another. There are always infinite choices for travel, but not all routes are created equal. Programs offering an economy of length and information are important to multiple fields. This chapter examines the economy issues surrounding reversible pathways. 

DIFFERENT THERMODYNAMIC PATHWAYS WITH IDENTICAL ENDPOINTS... 

Thermodynamic pathways describe programs for taking a system from one state to another. There is always an infinite number of choices, some more attractive than others in their economy. This chapter discussed how to evaluate pathways for both length and information economy using merit factors. The smaller Q, the better the overall economy. =0 offers the maximum economy, whereas = ° describes the worst case. 

At present, more than 100 different mechanisms describing possible oxidation pathways of water to molecular oxygen have been documented. Possible thermodynamic pathways of water oxidation to molecular oxygen are illustrated in Fig. 30 [81]. 

The result showed that, compared with the intramolecular Sn2 attacking to construct a seven-membered ring, acyl transferring from primary to secondary hydroxyl through a six-membered ring transition state (Fig. 3.20) was more favor in dynamic and thermodynamic pathway. Thus, the intramolecular 8 2 strategy was difficult to realize. 

Thermodynamic Path and Endpoint. The specification of the endpoint and the thermodynamic pathway used to reach the endpoint is important to the development of the source model. If, for instance, initially quiescent fluid is accelerated during a release, and the endpoint is defined as moving fluid, then the assumption of an isentropic pathway is normally valid. If, however, the endpoint is defined as quiescent fluid (for example, a pool of liquid after a release), independent of any transient accelerations, then the initial and final enthalpies would be assumed equal (this does not irnply that the enthalpy is constant during the release process). 

The thermodynamic pathway shown in Figure 5.4 can be proposed to describe the adsorption of a gas at equilibrium from the given standard state For step 1 the change in standard free energy is ... 

GCMC simulations have also been used to explore the favorable thermodynamic conditions for exchanging carbon dioxide and methane in the S-I clathrate hydrates. Of practical interest is the need to find a feasible thermodynamic pathway in the phase diagram consisting of methane, carbon... 

We typicallyknowthe enthalpy (heat) and entropy offiision at aspecifted temperature— the normal melting point, T. Therefore, we need to construct a thermodynamic pathway to find the enthalpy and entropy of fusion at any T. Figure 8.19 illustrates a path for the calculation of Ahfus- Adding together the three steps, we get ... 

The drawing on the cover fllustrates a central theme of the book using molecular concepts to reinforce the development of thermodynamic principles. The cover illustration depicts a turbine, a common process that can be analyzed using thermodynamics. A cutaway of the physical apparatus reveals a hypothetical thermodynamic pathway marked by dashed arrows. Using this text, students will learn how to construct such pathways to solve a variety of problems. The hgure also contains a molecular dipole, which is drawn in the PT plane associated with the real fluid. By showing how principles of thermodynamics relate to concepts learned in prior courses, this text helps students construct new knowledge on a sohd conceptual foundation. 

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