Secondary equilibria kinetics

A different experimental approach to the relative importance of one-center and two-center epimerizations in cyclopropane itself was based on the isomeric l-13C-l,2,3-d3-cyclopropanes165"169. Here each carbon has the same substituents, one hydrogen and one deuterium, and should be equally involved in stereomutation events secondary carbon-13 kinetic isotope effects or diastereotopically distinct secondary deuterium kinetic isotope effects may be safely presumed to be inconsequential. Unlike the isomeric 1,2,3-d3-cyclo-propanes (two isomers, only one phenomenological rate constant, for approach to syn, anti equilibrium), the l-13C-l,2,3-d3-cyclopropanes provide four isomers and two distinct observables since there are two chiral forms as well as two meso structures (Scheme 4). Both chiral isomers were synthesized, and the phenomenological rate constants at 407 °C were found to be k, = (4 l2 + 8, ) = (4.63 0.19)x 10 5s l and ka = (4kl2 + 4, ) = (3.10 0.07) x 10 5 s 1. The ratio of rate constants k, kl2 is thus 1.0 0.2 both one-center and two-center... 

A major criticism of the stochastic probability approach is that relatively slow secondary reactions, for which the near-equilibrium assumption does not apply, cannot be accommodated. In this situation, it is necessary to derive and solve simultaneous partial differential equations for mass conservation and obtain expressions for the first and second moments of the elution profile and the concomitant plate height arising from slow kinetics of secondary equilibrium. If, once again, the process can be represented as involving the reversible binding of two forms, the resolution of the interconverting species can be given by [59]... 

The magnitude of -deuterium equilibrium isotope effects The magnitude of the p-secondary deuterium kinetic isotope effects in solvolyses which proceed via a cationic transition state have been shown to be conformationally dependent (Sunko and Hehre, 1983). Shiner furnished two important representative examples relating the dihedral angle between an adjacent C—H or C—D bond and the vacant p-orbital of the cationic transition state with the magnitude of the kinetic isotope effect. In the... 

The differenee in reaction rates of the amino alcohols to isobutyraldehyde and the secondary amine in strong acidic solutions is determined by the reactivity as well as the concentration of the intermediate zwitterions [Fig. 2, Eq. (10)]. Since several of the equilibrium constants of the foregoing reactions are unknown, an estimate of the relative concentrations of these dipolar species is difficult. As far as the reactivity is concerned, the rate of decomposition is expected to be higher, according as the basicity of the secondary amines is lower, since the necessary driving force to expel the amine will increase with increasing basicity of the secondary amine. The kinetics and mechanism of the hydrolysis of enamines demonstrate that not only resonance in the starting material is an important factor [e.g., if... 

The dynamics of interstrand hole transport have also been investigated for several hairpins possessing GACC hole transport sequences in which a GG secondary donor is located in the complementary strand [41]. Kinetic data for 4GACC are reported in Fig. 9 and the resulting equilibrium data in Table 1. Comparison of the values of kt for 4GACC and 4GAGG shows that there is a kinetic penalty of 1/6 for inter- vs intrastrand hole transport. A... 

A catalyst used for the u-regioselective hydroformylation of internal olefins has to combine a set of properties, which include high olefin isomerization activity, see reaction b in Scheme 1 outlined for 4-octene. Thus the olefin migratory insertion step into the rhodium hydride bond must be highly reversible, a feature which is undesired in the hydroformylation of 1-alkenes. Additionally, p-hydride elimination should be favoured over migratory insertion of carbon monoxide of the secondary alkyl rhodium, otherwise Ao-aldehydes are formed (reactions a, c). Then, the fast regioselective terminal hydroformylation of the 1-olefin present in a low equilibrium concentration only, will lead to enhanced formation of n-aldehyde (reaction d) as result of a dynamic kinetic control. 

Spectroscopic and kinetic investigations of the reactions between 4,6-dinitrobenzofuroxan, 4-nitrobenzofuroxan, and tertiary and secondary amines (i.e., l,4-diazabicyclo[2.2.2]octane, quinuclidine, l,8-diazabicyclo[5.4.0]undec-7-ene, and piperidine) indicate the formation of zwitterionic or anionic complexes (Equation 2). The equilibrium between zwitterionic and anionic complexes is discussed (for reaction with piperidine) on the basis of H NMR spectral data, which indicate the presence of anionic complexes arising from the zwitterionic complex by a fast proton departure. The stability and the rate of formation of title complexes are discussed and compared to similar reactions of 1,3,5-trinitrobenzene <2001J(P2)1408>. 

The kinetic measurements must be accompanied by conductivity measurements, and the electrochemistry, i.e., the composition of the ionic population, and any equilibrium constants such as KD must be established by measurements during and after polymerisation and with model compounds, and secondary effects, such as that of m on Kd, must be investigated. 

In one of these studies, Kurz and Frieden (1980) observed the first unexpectedly large secondary a-deuterium KIE. They found that the secondary a-deuterium KIE for the nonenzymatic hydride ion reduction of 4-cyano-2,6-dinitrobenzenesulfonate by NADH (reaction (44)) was 1.156 0.018 and 1.1454 0.0093 using direct and competitive kinetic methods, respectively. The corresponding equilibrium isotope effects (EIEs) were found to be 1.013 0.020 and 1.0347 0.0087, respectively. Thus, the secondary deuterium KIE was much larger than the EIE. The magnitude of a secondary a-deuterium KIE is normally attributed to the rehybridization of the a-carbon that takes place when the reactant is transformed into the... 

An important property of the S-nitroso thiourea derivatives is the ability to effect electrophilic nitrosation of any of the conventional nucleophilic centres. This is manifest kinet-ically by the catalysis of nitrous acid nitrosation effected by added thiourea (equation 29). The situation is completely analogous to the catalysis of the same reactions by added halide ion or thiocyanate ion. The catalytic efficiency of thiourea depends on both the equilibrium constant Xxno for the formation of the intermediate and also its rate constant k with typically a secondary amine65. Since Xxno is known (5000 dm6 mol-2), it is easy to obtain... 

Salt effects in kinetics are usually classified as primary or secondary, but there is much more to the subject than these special effects. The theoretical treatment of the primary salt effect leans heavily upon the transition state theory and the Debye-Hii ckel limiting law for activity coefficients. For a thermodynamic equilibrium constant one should strictly use activities a instead of concentrations (indicated by brackets). 

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