[en] This paper presents the results of the radiometric analysis of the products of the degradation of 2-methylbutane formed in the isomerization of pentanes labeled with C 14 in the 1, 2, and 3 positions of the molecule. To determine the number of hydrogen atoms undergoing exchange during a single activation of the hydrocarbon molecule by the catalyst, the authors subjected a mixture of quasiequilibrium composition consisting of pentane and 2-methyl-butane-d₁₂ to isomerization at 125 C in the presence of A1C1₃. It is shown that the use of the isotopes H 2 and C 14, which enables one to observe the formation of not only skeletal isomers, but other products of isotopic exchange, clearly proves the difference in the mechanisms of isomerization over such catalysts of the same type as aluminum chloride and bromide