The Reaction of Methylcyclopentane with Hg 6(3P1) Atoms

The reaction of methylcyclopentane with photo‐excited Hg 6(³P₁) atoms was investigated in a static system at 29.35±0.01°C, over a range of initial pressures of 5–110 mm. After an initial slight pressure rise, the reaction exhibited a linear pressure decrease, the magnitude of which increased linearly with initial pressures of methylcyclopentane above 15 mm. The average rate of hydrogen formation also increased with initial pressure of methylcyclopentane and decreased with time in the course of a run. The products found were hydrogen, methylcyclopentenes, and a heavy fraction with the formula C₁₂H₂₂. Upon the basis of chemical and physical properties, strengthened by kinetic considerations, it was concluded that the C₁₂H₂₂ compound was predominantly dimethyldicyclopentyls. Quantum yields reached a maximum of 0.44 for hydrogen formation and 0.42 for methyl‐cyclopentane consumption. The mechanism postulated proceeds through an initial carbon‐hydrogen bond split, thus: $$\text{(1)\hspace{0.17em}\hspace{0.17em}}\mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{12}+\mathrm{Hg}{\text{\hspace{0.17em}6(}}^3{P}_1\mathrm{)\hspace{0.17em}\hspace{0.17em}\to }\mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{11}+\mathrm{H}+\mathrm{Hg}{\text{\hspace{0.17em}6(}}^1{S}_0)$$ $$\text{(2)\hspace{0.17em}\hspace{0.17em}}\mathrm{H}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}+}\mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{12}\to {\mathrm{H}}_2\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}+}\mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{11}$$ $$\text{(3)\hspace{0.17em}\hspace{0.17em}}\mathrm{H}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}+}\mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{11}\to \mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{12}$$ $$\text{(4)\hspace{0.17em}\hspace{0.17em}}\mathrm{H}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}+}\mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{11}\to \mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{10}+{\mathrm{H}}_2$$ $$\text{(5)\hspace{0.17em}\hspace{0.17em}}\mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{11}+\mathrm{cyclo}\hspace{0.17em}{\mathrm{C}}_6{\mathrm{H}}_{11}\to {\mathrm{C}}_{12}{\mathrm{H}}_{22}$$ $$\text{(6)\hspace{0.17em}\hspace{0.17em}}{\mathrm{H}}_2\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}+}\mathrm{Hg}{\text{\hspace{0.17em}6(}}^3{P}_1\mathrm{)\hspace{0.17em}\hspace{0.17em}\to }\mathrm{H}+\mathrm{H}+\mathrm{Hg}{\text{\hspace{0.17em}6(}}^1{S}_0)$$ This mechanism yields rate expressions which confirm the trends observed in the experimental work.