A group-contribution method for the calculation of the enthalpies of formation of free radicals and the dissociation energies of chemical bonds Communication 4. Saturated cyclic compounds

1986 ◽  
Vol 35 (5) ◽  
pp. 1016-1019 ◽  
Author(s):  
Yu. D. Orlov ◽  
Yu. A. Lebedev
Keyword(s):  
Free Radicals ◽  
Group Contribution ◽  
Enthalpies Of Formation ◽  
Chemical Bonds ◽  
Group Contribution Method ◽  
Dissociation Energies ◽  
Cyclic Compounds

Bond Energies

2008 ◽  
Author(s):  
José A. Martinho Simões ◽  
Manuel Minas da Piedade
Keyword(s):  
Driving Forces ◽  
Theoretical Models ◽  
Enthalpies Of Formation ◽  
Chemical Bonds ◽  
Bond Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Or Groups ◽  
Quantum Chemistry Calculations ◽  
Standard Enthalpies Of Formation

Although standard enthalpies of formation provide information about the net stability of molecules and their transformations, they do not always indicate stability of individual bonds. This analysis normally involves parameters, loosely called “bond energies,” that reflect the amount of energy required to cleave chemical bonds. Bond energies are essential for understanding the nature of chemical bonds. They can be used to assess the results from quantum chemistry calculations (or from other, less sophisticated theoretical models) and thus support or oppose the descriptions of those bonds. Moreover, bond energy values also enable us to estimate the driving forces of chemical reactions by considering the strengths of all the bonds that are cleaved and formed. In fact, there are many reactions for which the standard enthalpies of formation of all reactants and products are not available (and cannot be easily estimated) but whose energetics can be predicted from the appropriate bond energies. In the previous chapters, we attempted to review all the important parameters in molecular energetics, but to avoid unnecessary distraction, we deliberately omitted bond energies from the discussion. The literature is plagued with a variety of concepts that fall into that designation but are not always synonymous. We can find names like bond strengths, bond enthalpies, bond energies, bond dissociation enthalpies, bond dissociation energies, bond disruption enthalpies, bond enthalpy terms, intrinsic bond energies, and symbols like D, D̄, 〈D〉, E, BDE, and so on. The meaning of these concepts it not always obvious and, unfortunately, some are occasionally misused. Now we look into each one of them. Consider a molecule AB, where A and B can be atoms or groups of atoms.

scholarly journals Temperature-dependent estimation of Gibbs energies using an updated group contribution method

2018 ◽  
Author(s):  
Bin Du ◽  
Zhen Zhang ◽  
Sharon Gruber ◽  
James T. Yurkovich ◽  
Bernhard O. Palsson ◽  
...  
Keyword(s):  
Metal Ion ◽  
Equilibrium Constants ◽  
Binding Constants ◽  
Entropy Change ◽  
Group Contribution ◽  
Mass Action ◽  
Enthalpies Of Formation ◽  
Standard Entropy ◽  
Group Contribution Method ◽  
Reaction Equilibrium

AbstractReaction equilibrium constants determine the mass action ratios necessary to drive flux through metabolic pathways. Group contribution methods offer a way to estimate reaction equilibrium constants at wide coverage across the metabolic network. Here, we present an updated group contribution method with: 1) additional curated thermodynamic data used in fitting; and 2) capabilities to calculate equilibrium constants as a function of temperature. We first collected and curated aqueous thermo-dynamic data, including reaction equilibrium constants, enthalpies of reaction, Gibbs free energies of formation, enthalpies of formation, entropies change of formation of compounds, and proton and metal ion binding constants. We further estimated magnesium binding constants for 618 compounds using a linear regression model validated against measured data. Next, we formulated the calculation of equilibrium constants as a function of temperature and calculated necessary parameters, including standard entropy change of formation (ΔfS∘) and standard entropy change of reaction (ΔrS∘), using a model based on molecular properties. The median absolute errors in estimating ΔfS∘ and ΔrS∘ were 0.010 kJ/K/mol and 0.018 kJ/K/mol, respectively. The efforts here fill in gaps for thermodynamic calculations under various conditions, specifically different temperatures and metal ion concentrations. These results support the study of thermodynamic driving forces underlying the metabolic function of organisms living under diverse conditions.

Mechanochemical Phenomena in Polymers. II. The Effects of Initiators and Inhibitors of Chain Processes

1963 ◽  
Vol 36 (2) ◽  
pp. 480-487
Author(s):  
E. V. Reztsova ◽  
B. T. Kipkina ◽  
G. L. Slonimskii
Keyword(s):  
Free Radicals ◽  
Fatigue Resistance ◽  
Substantial Effect ◽  
Chemical Bonds ◽  
Chain Processes ◽  
Radical Processes ◽  
Effect Of Inhibitors ◽  
Dynamic Fatigue

Abstract 1. The substantial effect of inhibitors and initiators of chain radical processes on the change in the properties of rubbers in milling, as well as on the resistance of vulcanizates to fatigue, has been shown. This indicates a mechanochemical mechanism for processing of polymers and in the fatigue of elastomers. The act of mechanical scission of chemical bonds, with the formation of free radicals which initiate the secondary chain processes, rests on these processes. 2. The possibility has been shown of regulating the properties of polymers during processing, and also of increasing the dynamic fatigue resistance of vulcanizates by incorporating small quantities of additives active in regard to free radicals.

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