Negative kinetic temperature effect

Another m3d h arises from the intuition that pressure effect is opposite to the temperature effect. This is not true in kinetics. Therefore, kinetic constants (reaction rate constants, diffusion coefficients, etc.) almost always increase with increasing temperature, but they may decrease or increase with increasing pressure. Both positive and negative pressure dependences are well accounted for by the transition-state theory and are not strange. 

Rates of BTPPD oxidation of vicinal and non-vicinal diols (and one of their monoethers) in DMSO/TsOH to the corresponding hydroxyaldehyde are first order in BTPPD, second order in diol and H+, and correlated with Taft s Ea values with negative p. A symmetrical transition state in the rate-determining step is suggested from the temperature dependence of the kinetic isotope effect (kjj/kp = 6.61 using [l,l,2,2- H4]ethanediol). The cation-solvating power of the solvents is indicated from the analysis of the solvent effect in ethanediol. A mechanism involving formation of chromate ester in a pre-equilibrium is postulated. ... 

It has long been known that substitution at the anion of Zeise s salt, [Pt(CH=CH2)Cl3], is, thanks to the high trans effect of the coordinated ethene, very fast. Recent developments in low-temperature stopped-flow apparatus have now permitted the study of the kinetics of substitution at Zeise s and other [Pt(alkene)Cl3] anions in methanol solution. These substitutions obey the customary two-term rate law (i.e. with kohs = ki+ /s3[nucleophile]), with large negative AS values for the k2 term as expected for Sn2 processes (196). 

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