It is shown that octene-1 adsorbed on zeolite H-ZSM-5 at ambient temperature exhibits carbenium ion properties. Namely : (1) According to H-2 NMR, the proton of the acidic =A1-OH-Si= group of the zeolite is transferred into the CH2= group of the octene-1 molecule. (2) According to C-13 NMR the C-13 label inserted into the terminal CH2= group of the octene-l molecule is scrambled over its hydrocarbon skeleton. Thermodynamic and kinetic parameters for carbon scrambling are measured within the temperature range 290-343 K. The zeolite framework is shown to favour the formation of the linear rather than branched carbenium ion.