111. The theory of isotope effects has progressed to the point where it is feasible to design experiments in which the spin and mass isotope effects anticipated on chemicul grounds should be in opposite directions. This does not appear to be the case for recently reported photoinduced carbon-13 enrichments in dibenzyl ketone2a. c% e and phenylbenzoate. 2b In both cases the heavier isotope appears preferentially where it would be expected if a ...
