Arrhenius parameters with carbonyls

The effect of ring substituents on the rate constants, deuterium kinetic isotope effects and Arrhenius parameters for ene-additions of acetone to 1,1-diphenylsilane have been explained in terms of a mechanism involving fast, reversible formation of a zwitterionic silene-ketone complex, followed by a rate-limiting proton transfer between the a-carbonyl and silenic carbon. A study of the thermal and Lewis acid-catalysed intramolecular ene reactions of allenylsilanes with a variety of... 

Rate constants and Arrhenius parameters for the reaction of Et3Si radicals with various carbonyl compounds are available. Some data are collected in Table 5.2 [49]. The ease of addition of EtsSi radicals was found to decrease in the order 1,4-benzoquinone > cyclic diaryl ketones, benzaldehyde, benzil, perfluoro propionic anhydride > benzophenone alkyl aryl ketone, alkyl aldehyde > oxalate > benzoate, trifluoroacetate, anhydride > cyclic dialkyl ketone > acyclic dialkyl ketone > formate > acetate [49,50]. This order of reactivity was rationalized in terms of bond energy differences, stabilization of the radical formed, polar effects, and steric factors. Thus, a phenyl or acyl group adjacent to the carbonyl will stabilize the radical adduct whereas a perfluoroalkyl or acyloxy group next to the carbonyl moiety will enhance the contribution given by the canonical structure with a charge separation to the transition state (Equation 5.24). 

Formyl fluoride decomposes in a Teflon reaction vessel at 125-200 °C to hydrogen fluoride and carbon monoxide by a first-order process. Arrhenius parameters are A = 2x 10 sec , = 10 kcal.mole . Fischer and Buchanan have proposed that the decomposition is homogeneous and unimolecular and that the unusually low values for the Arrhenius parameters are associated with a multiplicity change in the carbonyl group in the transition state. 

Atmospheric chemistry demands have given a nuuked stimulus to studies of reactions of 0 atoms and OH- radicals with atmospheric substrates at about room temperature and below. Reactions of O atoms with alkenes and aromatics are important in photochemical smog formation and control. Rate constants, and in many cases Arrhenius parameters, are available for a variety of -O atom reactions with alkenes, alkynes, aromatics, unsaturated aldehydes, alkanes, - and carbonyl compounds. In general, the rate constants refer to the ovoall process ... 

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