In the chain oxidation processes two elementary reactions, alkyl radical addition to molecular oxygen and peroxy radical recombination, are shown to be spin selective and isotope sorting. The ratio of the radical addition rate constants k(a)((OO)-O-17-O-16)/k(a)((OO)-O-16-O-16) for alkyl radical from ethylbenzene is found to be 1.011; i.e., (OO)-O-17-O-16 molecules react 1.1% faster than O-16(2) molecules. For the O-18 nuclei only the classical isotope effect operates, producing the enrichment of molecular oxygen with O-18 nuclei. The ratio of the rate constants k(a)((OO)-O-18-O-16)/k(a)((OO)-O-16-O-16) for the same alkyl radical is 0.990; i.e., (OO)-O-18-O-16 molecules react 1% slower than O-16(2) molecules. In the peroxy radical recombination the magnetic isotope effect induces the regeneration of O-17-enriched oxygen molecules, resulting in the enrichment of the remaining molecular oxygen with O-17 magnetic nuclei. The ratio of the chain termination rate constants k(RO(17)O+(16)OOR)/k(RO(16)O+(16)OOR) is found to be 1.8 +/- 0.1 for the polymer oxidation.