Cyclopentane isotopic distributions

FIG. 3. Effect of temperature (°C) on the isotopic distribution patterns (di-dio) resulting from exchange of cyclopentane on a Pd/A Oj catalyst. The paterns are normalized to 1.0 at the dio isomer (1). Reprinted with permission from Accounts Chem. Res. 2, 289 (1969). Copyright by the American Chemical Society. 

A run with toluene seems to have no effect upon a subsequent run with hexene and hydrogen. Run 158 of Table V was followed by a run with toluene and hydrogen. Run 158 was then repeated with very little change from the results reported in Table V. The same result was obtained in a run with benzene at 80° sandwiched between two runs with cyclopentane on a microcrystalline catalyst. This was run 280. Data on runs 288 and 290 are given in Section VII, G. The isotopic distribution pattern of the benzene was almost exactly random. 

The previous work on cyclopentane (10) resulted in isotopic distribution patterns like run 290 of Table X, which exhibits a maximum at perdeuterocyclopentane. However, only twice as many molecules exchanged by single-atom as by many-atom exchange in run 290, whereas on the previous catalyst (10) the ratio was 16. Our previous patterns (10) seem, however, generally characteristic of microcrystalline catalysts. Many-atom exchange with the amorphous catalysts, runs 285 and 296, leads to a distribution in which Di is constant between i equal 3 to 7 followed by a decline in Di with a minimum at the perdeutero. 

That propane is indeed formed by H2 reaction is known by observing the distribution of yields of various isotopic compositions of propane from the radiolysis of an equimolar mixture of cyclopentane and deuterated cyclopentane. Further evidence is provided by the facts that (1) propane is not formed by photolysis below the ionization threshold, and (2) an electric field has no effect on the yield. 

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