MAGNETIC AND CLASSICAL OXYGEN-ISOTOPE EFFECTS IN CHAIN OXIDATION PROCESSES - A QUANTITATIVE STUDY

In the chain oxidation processes two elementary reactions, alkyl radic al addition to molecular oxygen and peroxy radical recombination, are shown to be spin selective and isotope sorting. The ratio of the radic al addition rate constants k(a)((OO)-O-17-O-16)/k(a)((OO)-O-16-O-16) f or 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 en richment of molecular oxygen with O-18 nuclei. The ratio of the rate c onstants 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 is otope effect induces the regeneration of O-17-enriched oxygen molecule s, resulting in the enrichment of the remaining molecular oxygen with O-17 magnetic nuclei. The ratio of the chain termination rate constant s k(RO(17)O+(16)OOR)/k(RO(16)O+(16)OOR) is found to be 1.8 +/- 0.1 for the polymer oxidation.