Complexes and Negative Activation Energies in Arylhalocarbene/Alkene Additions: Activation Parameter Dependence on Alkane Solvent Chain Length

Abstract

Activation parameters for the additions of PhCCl, F-PhCCl, and 3,5-dinitro-PhCCl to tetramethylethylene, cyclohexene, and 1-hexene have been determined in decane. With the exception of two carbene/alkene combinations, Arrhenius correlations of ln k vs 1/T were unimodal and linear, affording negative activation energies and entropies. The additions of PhCCl or F-PhCCl to 1-hexene gave bimodal Arrhenius correlations. Comparisons to the analogous experimental data obtained in pentane and computational studies help to elucidate the observed behavior. Activation entropies decrease in parallel with activation enthalpies going from pentane to decane solvent, suggesting that enthalpy-entropy compensation is operative in these carbene additions. The bimodal Arrhenius behavior is proposed to result from carbene-alkene additions taking place intrinsically or extrinsically to decane solvent cage assemblies.

Latent Porosity in Alkali-Metal M2B12F12 Salts: Structures and Rapid Room-Temperature Hydration/Dehydration Cycles

“…For Cs 2 Z, rh max decreased by nearly 8 times as the temperature increased from 24.0 to 32.0 °C (see Table S29). This so-called “negative kinetic temperature effect”, sometimes said to indicate “a negative activation energy”, is uncommon in condensed-phase chemical kinetics in general − and is only rarely encountered in solid-state reactions. − In solution, an apparent negative activation energy can be due to an equilibrium prior to the rate-determining step that shifts to the left with increasing temperature. In the case of the hydration of M 2 Z salts, it is possible that a surface hydration equilibrium controls the overall rate of hydration.…”

Hydroxyl‐initiated oxidation processes of phenylenediamines treated by the atmospheric plasma: A theoretical study in gas phase

“…However, reactive complexes could not be responsible for all negative activation energies because no stable complex could be obtained. Thus, entropic factor was introduced to explain the carbene/alkene additions [39,40]. For bulk solution, the activation energy E a = ΔH + RT.…”