Temperature dependence, exchangeable proton signals

The proportions of oxonium and carbenium ions in the chain growth, as well as their relative reactivities, may markedly depend on the polymerization coixlitions and vary with monomer structure. The high values of rate constants of the reaction between carbenium cations and ethers or acetals make questionable Okada s interpretation of the 1,3-dioxane-triethyloxonium salts system It is impossible to observe, at room temperature, the individual ROCHl species with excess of such nucleophiles as diethyl ether. We would rather suggest that the signal at 11—13 ppm 6 ( H-NMR) or 175—180 ppm 6( C-NMR) is due to some exchanging protonated species. 

A further rise of temperature to -f 50 °C broadened and merged the signal of the ring protons from the mesitylenium ion and mesitylene with that of HF by the exchange process (1) with the HFj"" anion. The temperature dependence of the PMR... 

Ishikawa et detected the free-induction signals of xenon atoms polarized by spin-exchange optical pumping. The temperature dependence of dissolution and spin-polarization transfer of xenon atoms in ethanol is measured by simultaneous detection of both xenon and ethanol protons. 

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