Changeover in mechanism

Ronlin et al., 1973). A recent kinetic investigation produced a number of interesting results (Aalstad et al., 1981b). A nearly complete changeover in mechanism, from radical cation dimerization at high concentrations to radical... 

Confirmation for the changeover in mechanism is found in the fact that during the first 100 hours, vinyl is... 

Since substitution reactions of square-planar complexes in most cases tend to follow an associative mechanism, a large number of complexes were synthesized in efforts to determine whether a changeover in mechanism is induced. The increase in steric hindrance caused by introducing alkyl substituents on the three N donor atoms of diethylenetriamine (dien) in going from dien to Mesdien to Etsdien, caused a decrease in the aquation rate constant for [Pd(Rsdien)Cl]+ of six orders of magnitude, but not a changeover in mechanism. The reported activation... 

In other complexes the introduction of a C atom as a strong u-donor ligand, increases the reactivity of Pt(II) by six orders of magnitude compared to [Pt(H20)4] , but does not induce a changeover in mechanism. Surprisingly, there is only one example in the literature where the authors report activation volumes in support of a changeover in the substitution mechanism, i.e. from the usual associative to the unusual dissociative mechanism. The authors point out that at least two strong... 

Dimethyl-4-pyridone exchanges as the free base at lower acidities but as the conjugate acid at acidities above H, -3.5. A similar changeover in mechanism occurs at -2.7 for l,2,6-trimethyl-4-pyridone. A comparison of rate data from l,2,6-trimethyl-4-pyridone, 4-methoxy-2,6-dimethylpyridine and... 

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