Thermochemical parameters

THERM Thermodynamic Property Estimation for Radicals and Molecules, Edward R. Ritter and Joseph Bozzelli, Int. J. Chem. Kinet. 23, 767-778, (1991). A computer program for IBM PC and compatibles for estimating, editing, and entering thermodynamic property data for gas-phase radicals and molecules using Benson s group additivity method. 

RADICALC Bozzelli, J. W. and Ritter, E. R. Chemical and Physical Processes in Combustion, p. 453. The Combustion Institute, Pittsburgh, PA, 1993. A computer code to calculate entropy and heat capacity contributions to transition states and radical species from changes in vibrational frequencies, barriers, moments of inertia, and internal rotations. 

FITDAT Kee, R. J., Rupley, F. and Miller, J. A. Sandia National Laboratories, Livermore, CA 94550. A Fortran computer code (fitdat.f) that is part of the CHEMKIN package for fitting of species thermodynamic data (cp, h, s) to polynomials in NASA format for usage in computer programs. 

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Before delving into experimental methodology, it is useful to recall the definitions of common thermochemical parameters. A detailed description of thermochemical properties is available. ... 

A mass spectrometer can be also used as a gas phase laboratory and a lot of reactions can be done inside it. Furthermore chemico-physical properties, such as proton affinity, the energetics of gas phase processes and many other thermochemical parameters can be... 

Co2(CO)q system, reveals that the reactions proceed through mononuclear transition states and intermediates, many of which have established precedents. The major pathway requires neither radical intermediates nor free formaldehyde. The observed rate laws, product distributions, kinetic isotope effects, solvent effects, and thermochemical parameters are accounted for by the proposed mechanistic scheme. Significant support of the proposed scheme at every crucial step is provided by a new type of semi-empirical molecular-orbital calculation which is parameterized via known bond-dissociation energies. The results may serve as a starting point for more detailed calculations. Generalization to other transition-metal catalyzed systems is not yet possible. 

Thermochemical parameters of some unstable nitrile oxides were evaluated using corresponding data for stable molecules. Thus, for 2,4,6-trimethylbenzo-nitrile N-oxide and 2,4,6-trimethoxybenzonitrile N-oxide, the standard molar enthalpies of combustion and sublimation at 298.15 K were measured by static-bomb calorimetry and by microcalorimetry, respectively, this made it possible to derive the molar dissociation enthalpies of the N—O bonds, D(N—O) (17). 

The transition-state theory (TST) provides the framework to derive accurate relationships between kinetic and thermochemical parameters. Consider the common case of the gas-phase bimolecular reaction 3.1, where the transient activated complex C is considered to be in equilibrium with the reactants and the products ... 

Thermochemical parameters estimated by semiempirical AMI calculations have been found to support the proposal that isobutene formation on gas-phase thermolysis of iV-methyl-A-phenyl-fert -butylsulfenamide and morpholinyl-ferf -butylsulfenamide occurs by a unimolecular mechanism involving a four-centre cyclic transition state and co-formation of the corresponding thiohydroxylamines." ... 

A paper by Miodownik (1986) suggested that significant changes in some of the thermochemical parameters could be obtained by adopting different entropies of... 

TABLE 9.7. ExperimentaF and Theoretical Thermochemical Parameters for 2-Naphthyl(methoxycarhonyl)carhene (17) ... 

Kinetic Thermochemical Parameters for the Decomposition of Molten and Liquid Explosives... 

It should also be noted that significant progress has been made in the measuring of thermochemical parameters of organozinc complexes. Ionization energies were measured and the dissociation characteristics of ions were determined. The experimental results for gaseous Zn-containing ions were supported by quantum-chemical calculations. 

A quantitative experimental measurement of the thermochemical parameters for a series of tetrazoles was carried out by McEwan et al. <1951JA4725, 1957JPC26>. These studies performed over 50 years ago are regarded as classical (Table 12) <1999THS(3)467>. 

In Table 13, results are compiled on evaluation of the A//f° values for some tetrazoles, published 20 years later by Lebedev and co-workers . In this study, refined values of the thermochemical parameters measured with the use of precision calorimeters were reported. The refined data proved the high reliability of the experimental findings ol Me If wan el al. (Table 13) <1951JA4725, 1957JPC26>. 

One of the most important thermochemical parameters in ion chemistry is the proton affinity (PA) (equation 12), and considerable experimental and theoretical work has been carried out in the last 30 years to determine this property accurately. 

The problem of determining AG° for organic redox couples can usually be attacked experimentally by either electrochemical methods or gas-phase measurements of ionization potentials and electron affinities. In both approaches, we can in principle determine thermochemical parameters for one-electron oxidation (83) and reduction (84) of an organic species. 

This explains the fact that the flammability tests based on estimates of the thermochemical parameters of polymeric systems (by direct calorimetric or indirect measurements) have been gaining more and more preference recently. 

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