Following adsorption of cyclopentene onto H-mordenite at low temperatures an EPR spectrum was recorded at 77 K which can be unequivocally assigned to the radical cation of 1,2,3,4,5,6,7,8-octahydronaphthalene (9-octalin), since it is identical with the spectrum recorded from an authentic sample of 9-octalin following γ-irradiation in a CFCl₃ matrix. This radical shows an interesting dynamic behaviour in terms of a concerted inversion of both rings that modulates the pseudoaxial and pseudoequatorial coupling. On initial adsorption at 195 K the activation energy associated with this process is 14.4 kJ mol^–1(actually less than that measured in solution by ODMR) but which surprisingly increases to 28.3 kJ mol^–1 on warming the sample to 295 K. This is interpreted in terms of radicals located at differing adsorption sites.

A similar adsorption study of dimethylacetylene on this zeolite led, at 150 K, to the detection of a spectrum with an odd number of broadish lines and a spacing of ca. 10 G which we attribute to the formation of the tetramethylcyclobutadiene radical cation. On heating to 350 K, the spectrum of the hexamethylbenzene radical cation was observed.

A comparative study of these compounds in freon matrices at varying concentrations was also made in order to probe the chemical properties of their radical cations by an authentic and independent method.