Thermal Isomerization of Isopropyl-1,1,1-d3 Radicals

The unimolecular isomerization of isopropyl radicals was investigated by studying the thermal decomposition of pure CD₃CH₂CH₃ from 472° to 553°C. Isomerization of CD₃CHCH₃, was detected by measuring CD₂CHD formed from the isomerized radical. The net result of isomerization is reaction (14). $$\begin{array}{c}\text{(14)}{\mathrm{CH}}_3\mathrm{CH}{\mathrm{CH}}_3\mathrm{\to [}{\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{]\to }{\mathrm{C}}_2{\mathrm{H}}_4+{\mathrm{CH}}_3,\\ \text{(15)}{\mathrm{CH}}_3\mathrm{CH}{\mathrm{CH}}_3\to {\mathrm{CH}}_3\mathrm{CH}={\mathrm{CH}}_2+\mathrm{H}.\end{array}$$ It is found that isomerization of isopropyl up to 500°C proceeds at a rate, relative to decomposition via reaction (15), which can be described by k₁₄/k₁₅≤0.07. A mechanism which produces methyl and ethylene directly without intermediate isomerization gives k₁₄/k₁₅≤0.04 at 500°C. Contrary to other published estimates of k₁₄/k₁₅, the latter shows no downward trend with increasing temperature.