Discrimination between Molecular and Free-Radical Models of 1-Phenyldodecane Pyrolysis

Liquid-phase thermolyses of 1-phenyldodecane (PDD) with added tetralin-d₁₂allowed discrimination between molecular mechanisms and stepwise free-radical mechanisms. The incorporation of a deuterium label into the major pyrolysis product, toluene, proved that free-radical steps were kinetically significant since an intramolecular mechanism would proceed independently of the added tetralin and yield only protonated products. Quantitation of the fraction (DI) of toluene that was singly deuteriated as a function of the ratio (R) tetralin-d₁₂/PDD allowed convincing estimation of DI = 1.0 as R → ∞. This demonstrated that at infinite dilution of PDD in tetralin-d₁₂, all toluene formed with a deuterium label, suggesting that PDD thermolysis was entirely free-radical.