Reaction coordinate entropy

Rate coefficients and kinetic parameters for iododeboronation were determined for the benzene- and thiophene-boronic acids, and the results are given in Table 256. The relative reactivities derived from this work correlated well with those obtained in a number of other electrophilic substitutions572, which is perhaps surprising in view of the large variation in the entropies of activation. These differences were explained by Brown et al.132 in terms of the transition state for the phenyl compound occurring earlier along the reaction coordinate than for the... 

However, the rate of substitution of pyrrole is too high and that of benzene too low to be followed by standard techniques, and consequently a kinetic study was limited to furan, thiophene, selenophene, and tellurophene. Activation entropies are constant for all four members of the series, indicating that the arrangement of the atoms around the reaction center is similar, i.e., the transition states of all four rings occur at similar positions along the reaction coordinate. The relative rates for the formylation are thus controlled by the activation enthalpies. At 30UC relative rates are furan (107), thiophene (1), selenophene (3.64), and tellurophene (36.8).68... 

It has been suggested that an increase in the coordination number of vanadium from 4 to 5 already takes place in the second protonation step, i.e. when [H2V04] is formed (21). For reactions (1) and (2), however, the protonation constants and thermodynamic parameters are comparable with those reported for P04 and As04 , providing firm evidence that reaction (2) is not accompanied by incorporation of water in the vanadate ion (15, 17). Further, the estimated thermodynamic quantities for reaction (6), AH° = -39 kJ/mol and AS0 = —51 J/(mol K), obtained by extrapolation from the experimental values for reactions (1) and (2) and those for the three protonation steps of P04 and As04 , are not typical of a simple protonation reaction (17). For such a reaction the entropy change is normally a positive quantity often amounting to 100 50 J/(mol K) and the enthalpy... 

For the moment, we can consider the activated complex as a type of intermediate (although not isolatable) reached by the reactants as the highest energy point of the most favorable reaction path. The activated complex is in equilibrium with the reactants and is commonly regarded as an ordinary molecule, except that movement along the reaction coordinate will lead to decomposition. The activated complex can be assumed to have the associated properties of molecules, such as volume, heat content, acid-base behavior, entropy, and so forth. Indeed, formal calculations of equilibrium constants involving reactions of the activated complex to form another activated complex can be carried out (Sec. 5.6 (b)). ... 

These parameters (AG, A//, and A5 ) differ slightly from normal standard parameters in that the contribution of motion along the reaction coordinate toward the transition state is not included. The values are the difference in free energy, enthalpy, and entropy between 1 mole of activated complex and 1 mole of each reactant, all substances being at their standard-state concentrations (usually 1 M). 

Universal gas constant (R = 8.31447 J moU K ) if is given in J kg then the gas constant depends on the gas species Radial coordinate reaction rate Entropy... 

R. A. Marcus My interests in variational microcanonical transition state theory with J conservation goes back to a J. Chem. Phys. 1965 paper [1], and perhaps I could make a few comments. First, using a variational treatment we showed with Steve Klippenstein a few years ago that the transition-state switching mentioned by Prof. Lorquet poses no major problem The calculations sometimes reveal two, instead of one, bottlenecks (transition states, position of minimum entropy along the reaction coordinate) [2], and then one can use a method described by Miller and partly anticipated by Wigner and Hirschfelder to calculate the net dux. 

Short-lived organic radicals, electron spin resonance studies of, 5, 53 Small-ring hydrocarbons, gas-phase pyrolysis of, 4, 147 Solid state, tautomerism in the, 32, 129 Solid-state chemistry, topochemical phenomena in, 15, 63 Solids, organic, electrical conduction in, 16, 159 Solutions, reactions in, entropies of activation and mechanisms, 1, 1 Solvation and protonation in strong aqueous acids, 13, 83 Solvent effects, reaction coordinates, and reorganization energies on nucleophilic substitution reactions in aqueous solution, 38, 161 Solvent, protic and dipolar aprotic, rates of bimolecular substitution-reactions in,... 

Bimolecular reactions correspond to a negative entropy of activation. Note that AEfF, Aid , A S , AG , and A A all refer to an activated complex where the reaction coordinate is pulled out. 

Agmon N, Levine RD. Energy, entropy, and the reaction coordinate thermodynamic-like relations in chemical kinetics. Chem Phys Lett 1977 52(2) 197-201. 

In transition state theory, the rate of an adiabatic chemical reaction depends only on the difference between free energy in initial and transition states. From point of view of thermodynamics, formation of an intermediate complex can not give any preference to the process as compared with a collision complex. Nevertheless, the formation of a preliminary (pretransition) structure on the reaction coordinate can constrain the system of nuclear motions that do not lead to reaction products and, therefore, accelerate the process. It is necessary to stress that this acceleration is not caused by entropy reason, but by the optimization of the synchronization factor. 

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