Activation and free energy

The activity and free energy of water vapour H20(g) in equihbrium with the saturated solution of Ca(OH)2 are determined from eqn. (5.31)... 

A quantitative theory of rate processes has been developed on the assumption that the activated state has a characteristic enthalpy, entropy and free energy the concentration of activated molecules may thus be calculated using statistical mechanical methods. Whilst the theory gives a very plausible treatment of very many rate processes, it suffers from the difficulty of calculating the thermodynamic properties of the transition state. 

Tautomerism of 2-substituted hexahydropyrimidines has been studied (980PP53), and free energies, enthalpies, and entropies of activation for this ring-chain tautomeric equilibrium have been measured [97JCS(P2)169]. 

Activation Volume and Free Energy Calculated from Experimental Data... 

FIGURE 2.2 Optimized TS geometries of the cytosine alkylation reaction by o-QM, without and with water assistance. Bond lengths (in A) and activation Gibbs free energies (in kcal/mol) in the gas phase and in aqueous solution (in parentheses) at the B3LYP/6-311 +G(d,p)// B3LYP/6-31G(d) level of theory with respect to the reactants have been taken from Ref. [14]. 

The calculated potential and free energies for the first step of the four paths is presented in Table 3-2. As can be seen, the paths calculated with the combined procedure present activation energies of 17.77 and 16.85 kcal/mol for paths A and B respectively. On the other hand, the calculated potential activation energies are 20.37 kcal/mol for path C and 22.02 for path D. This is in contrast to the calculated... 

Reaction rate and free energy of activation, p. 37 2.2.2 Kinetics and the rate-limiting step, p. 39 2.2.3 Kinetic v. thermodynamic control, p. 42. 

In Table I are listed the first calculations (1961 8) of the enthalpy, entropy and free energy of activation at 298K. These are to be compared with the very recent (1980) calculations of Newton (11). 

Table 14 Arrhenius activation energies and free energies of activation (kcal mol ) for isomerization of substituted cyclopropanes in CDClj. ...

Park, H. and Lee, S. (2004) Homology modeling, force field design, and free energy simulation studies to optimize the activities of histone deacetylase inhibitors. Journal of Computer-Aided Molecular Design, 16, 375—388. 

All association rates are much slower than a diffusion controlled process, which would have a rate of about 109 M 1 sec-1 (134). However, the rates and free energies of activation seem to vary less from one system to another for the association than for the dissociation process. 

Table 4 Comparison of reaction pathway energetics (kcal/mol) for benzylperoxy radical and 2-picolinylperoxy radical at 298 K, via B3LYP/6-311+G //B3LYP/6-31G. Numbers refer to pathways depicted in Fig. 18. All enthalpies and free energies are relative to the peroxy radical (2) when preceded by TS, the relative data are the enthalpy and free energies of activation...

The stronger the solvating ability of a solvent is, the more it decreases the thermodynamic activity of the reactants and their reactivity, that is, their availability for the reaction. A linear correlation has been found between the activation Gibbs free energy of a series of Sn2 reactions and the acceptor number (AN) of the solvents (Marcus, 1998). 

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