Carbon−Hydrogen vs Carbon−Carbon Protonation in the Proton Transfer from Alkane Radical Cations to Alkane Molecules. A Study in γ-Irradiated CCl₃F/Decane at 77 K

A study is made of the formation of the isomeric chlorodecanes, and a search is made for shorter-chain 1-chloroalkanes (5 ≤ n C ≤ 9) formed in CCl 3 F/decane by γ-irradiation at 77 K and subsequent melting at various concentrations of decane. In such systems, proton transfer from decane radical cations to decane molecules resulting in the formation of pentacoordinated decane carbonium ions (protonated decanes) is quite extensive at high decane concentration, as is evidenced by the fact that under such conditions (i) the ESR spectrum of the irradiated system at 77 K largely consists of decyl radicals and (ii) the contribution of 1-chlorodecane to chlorodecane formation after melting the sample is quite small. The contribution of decyl radicals to the paramagnetic absorption sharply increases and the contribution of 1-chlorodecane to chlorodecane formation strongly decreases with increasing concentration of decane. It is observed that at high decane concentration formation of secondary chlorodecanes is extensive, with 2-chlorodecane being by far the most prominent, but that shorter-chain 1-chloroalkanes are essentially absent. From the results obtained it is concluded that proton transfer from decane radical cations to decane molecules in γ-irradiated CCl 3 F/decane results in the selective formation of secondary C−H protonated decanes with a clear preference for the penultimate position and that formation of C−C and primary C−H protonated decanes by this process is negligible.