Rate constants and activation energies for reaction of benzyl cation with ethers in solution: initial step in carbocationic polymerization

Abstract

Rate constants and activation energies for reactions of the benzyl cation with various ethers in solution have been determined by pulse radiolysis. These condensation reactions have activation energies slightly larger (by 0.3-2.0 kcal/mol) than the activation energies calculated for diffusion-limited ion-molecule reactions. Differences in the reactivities of the various ethers with the benzyl cation could be predominantly accounted for by the values of the preexponential factors rather than by the activation energies. Comparison of these rate constants with the relative basicity of the ethers obtained from steady-state systems showed a qualitative agreement.

Transient carbocations and carbanions generated by laser flash photolysis and pulse radiolysis

“…In addition, as a result of photolysis by the second laser pulse, depletion was noted in the region where the trityl radical absorbed. This result is also interesting in view of the fact that the trityl radical is recognized for intramolecular photochemistry, namely, electrocyclic ring closure to a dihydrofluorenyl-type radical, rendering its doubletdoublet fluorescence lifetimes short in fluid solvents (compared to long fluorescence lifetimes of the diphenylmethyl radical under similar conditions).109-111 H. Heterolytic Fragmentation, Including C-C Bond Cleavage In Radical Cations08, 108,[112][113][114][115][116][117][118][119][120][121][122] Certain radical cations, e.g., those containing relatively weak C-C bonds, undergo intramolecular fragmentation, leading to radicals and carbocations (eq 9).…”