Heptyl radicals formed by gamma-irradiation of n-C7H16, both in neat form and with various concentrations of n-C8D18 added before irradiation, are investigated by ESR spectroscopy. It is observed that the presence of deuterated octane in protiated heptane results in a substantial increase in the relative contribution of protiated l-heptyl radicals to the radical spectrum. Their formation is attributed to the proton-transfer reaction (n-C7H16.+ + n-C8D18 --> 1-C7H15. + n-C8D18H+) which, in accordance with an earlier and experimentally verified postulate stating that a strict relation exists between the radical site in alkyl radicals formed by proton transfer from alkane radical cations to alkane molecules and the structure of the semioccupied molecular orbital of the parent cation, is expected to yield 1-heptyl radicals selectively. The increase in the relative importance of 1-heptyl vs other isomeric heptyl radicals as a result of the presence of octane in heptane is confirmed by analysis of the tetradecanes formed by irradiation of heptane/1-chlorohexane (1 mol%) and heptane/1-chlorohexane (1 mol%)/octane (9 mol%) systems. As to the acceptor site, a study is made by gas chromatography of the yield and isomeric composition of chlorooctanes formed by gamma-irradiation of n-C7H16, containing 1 mol% 1-C6H13Cl and various concentrations of n-C8H18. Formation of chlorooctanes in such systems is largely due to neutralization of protonated octane molecules by chloride ions (C8H19+ + Cl- --> C8H17Cl + H-2) The isomeric composition yields direct information on the proton-acceptor site in the octane molecule. It is observed that mainly 2-chlorooctane is formed, with much smaller yields of 1- and 3-chlorooctane; the formation of 4-chlorooctane is still less pronounced.