Kinetic ratio

Treatment of A -benzyltnfluoroacetimidoyl chloride with triethylamine in toluene at room temperature leads to in situ generation of trifluoroacetonitrile ben-zylide [4J] (equation 43), which reacts with methyl acrylate to form cycloadducts [43] (equation 44) Although the kinetic ratio of products favors the cis adduct (3 1), thermodynamic equilibration leads to an excess of the trans isomer (7 1). 

It also explains the /Z selectivity of products at low conversions (kinetic ratio. Scheme 19). In the case of propene, a terminal olefin, E 2-butene is usually favoured (E/Z - 2.5 Scheme 19), while Z 3-heptene is transformed into 3-hexene and 4-octene with EjZ ratios of 0.75 and 0.6, respectively, which shows that in this case Z-olefins are favoured (Scheme 20). At full conversion, the thermodynamic equilibriums are reached to give the -olefins as the major isomers in both cases. For terminal olefins, the E olefin is the kinetic product because the favoured pathway involved intermediates in which the [ 1,2]-interactions are minimized, that is when both substituents (methyls) are least interacting. In the metathesis of Z-olefins, the metallacyclobutanes are trisubstituted, and Z-olefins are the kinetic products because they invoke reaction intermediates in which [1,2] and especially [1,3] interactions are minimized. 

The effectiveness of magnesium enolates as nucleophilic agents limits the interest of the reaction. With less substituted substrates (R = H), the aldol reaction is faster than the sily-lation. Moreover, due to solubility limitations, the authors are unable to determine whether the high thermodynamic kinetic ratio of silylenol ethers obtained accurately represents the magnesium enolate composition. Nonetheless, this method is an excellent procedure to selectively prepare the thermodynamic silylenol ether from an unsymmetrical ketone. ... 

The Hammond Postulate applies only if both forward reactions are fast. Obtain energies for the transition states leading to 1 -propyl and 2-propyl radicals (propane+F end andpropane+F center). Draw an energy diagram for each hydrogen abstraction reaction (place the diagrams on the same axes). Do these diagrams indicate that use of the Hammond Postulate is justified Calculate the barrier for each reaction, and calculate the relative concentrations of 1-propyl and 2-propyl radicals that would form at 298 K if each reaction were irreversible. Use equation (2). How does this (kinetic) ratio compare to the equilibrium (thermodynamic) ratio of these radicals ... 

There thenfollowed reports by Katz [13] and Grubbs [14] and their co-workers on studies that aimed to simplify and confirm the analysis. The key remaining issue was whether a modified pairwise mechanism, in which another alkene can coordinate to the metal and equilibrate with the product prior to product displacement, would also explain the appearance of the anomalous cross-over products early in the reaction evolution. However, a statistical kinetic analysis showed that for a 1 1 mixture of equally reactive alkenes, the kinetic ratio of cross-metathesis should be 1 1.6 1 for the pairwise mechanism and 1 2 1 for the Chauvin mechanism. Any equilibration (substrate or product) would, of course, cause an approach towards a statistical distribution (1 2 1) and thus allow no distinction between the mechanisms. 

The benzannulation reaction further allows the concomitant generation of an axial and chiral plane in a single reaction step (Scheme 28) [68f]. The diastereomeric ratio of the benzannulation products depends on the protocol used for phenol protection. Thus, in situ protection gives the kinetic ratio of 74a 74b — 11 89, whereas a two-step benzannulation/ protection sequence results in thermodynamic control to give a ratio of 74a 74b >99 1. These results can be explained in terms of a possible or arrested rotation around the biaryl axis in the benzannulation product before protection to give either 74a or 74b. 

The formal complex of an imine RCH=NR with a zirconocene of C2v symmetry will be formed as a racemic mixture, with equal amounts of two enantiomers. If a zirconaaziridine possesses another stereogenic element, it will have two diastereomers of unequal energy, and they may be generated in a kinetic ratio that is not equal to their thermodynamic ratio. 

Then, it can be concluded from these results that the smaller the surface area or micropore volume accessible to benzene, the higher ability of the CMS to discriminate between CO2 and CH4. On the other hand, the N2/O2 kinetic ratio also decreases (3.6 for CS-8), as can be expected from the widening of the porosity as determined by immersion calorimetry. 

A more thorough analysis of the enantioselectivity of several commercially available alkaline proteases was performed by determining the enantioselectivity fador E of these enzymes in the hydrolysis of (R,S)-4. In order to determine the enantioselectivity factor E accurately (the kinetic ratios for the conversion of the two enantiomers in a first-order kinetic resolution) [11], accurate measurement of the optical purity of the product acid and unreacted ester is necessary. Separation of the carboxylic acid enantiomers by gas chromatography was not possible due to decomposition of the acid on the column, so a derivatization method was developed to convert the acid into the corresponding methyl ester. Treatment of the extracted acid and ester with trimethylsilyldiazomethane resulted in the conversion of the acid into the methyl... 

An alternative to the concept of average kinetic temperature is the kinetic ratio (o), a ratio of a rate constant at a fluctuating temperature to that at a standard temperature, Tai ... 

The kinetic ratio can be used to represent the effect of temperature fluctuations.782... 

M. Scher, Kinetic ratio as a parameter for product stability calculations, J. Pharm. Sci. 69, 325-327 (1980). 

The data listed in Table 10.17 give clear evidence of the enormous rate acceleration in aqueous solution, in accordance with all previous kinetic reports [51, 61, 72), particularly for the corresponding cyclopentadiene cycloadditions [73]. The highest values for the kinetic ratio ks/fcref (> 1000) are observed for reactions involving the least hydrophilic molecules (HCCP -1- styrene, isoprene I-methyl acrylate, dimerization of isoprene). Intermediate values are found in reactions involving ketones. 

Hsieh, H.L., McKinney, O.E., 1966. Relationship between heterogeneity index and kinetic ratio of anionicaUy polymerized polymers. J. Polym. Sci. Polym. Lett. Ed. 4(11), 843-847. 

Salazar found that 1,3-dimethylenecyclopentane undergoes a degenerate rearrangement by both 1,3- and 3,3-sigmatropic shifts as judged by a 2 1 kinetic ratio of the appropriate deuterium isomers at 350°C (Scheme 8.42). ... 

Denominator 2 is valid only in the frame of linear mechanics which makes the kinetic energy equal to one half the product v P or IW i. In the nonlinear case, this denominator can be replaced by the reciprocal of an inductive energetic ratio here a kinetic ratio Pg, defined as follows ... 

By using the definition in Equation K4.27 of the kinetic ratio and by stating the equality between kinetic and volume energy, the following relationship between energetic ratios is obtained ... 

---