Exchange between Deuterium and Hexenes

The substitution of deuterium for hydrogen makes no change in the chemistry and little in the rates but it provides a large amount of information about the nature of the processes. Experimental data have been pre,sented in Section VI I,F. 

Process (9), cis-lrans Isomerization. As may be seen in Table VIII, trans-2-hexene is more heavily exchanged than cis-2-hexene. If, as suggested in Section IX,C, some of the raws-2-hexene results from isomerization of cis-2-hexene formed initially, one would expect the trans to be more extensively labeled. We assume tentatively that this suggestion is correct. 

Process (5), Isotopic Exchange of Reactant Hexene. However, the moles of hydrogen atoms from the positions equilibrated in 2-hexene is 0.108(0.65) =0.070. This is much too small a quantity to mix with 0.20 moles of deuterium atoms to give (D ) = 0.35 even if we allow for the extra hydrogen added to the pool in the isomerization of cis- to trans-2-hexene. The only other source of hydrogen is in exchanged 1-hexene. This provides approximately the needed ratio D/H, for (D ) = 0.35. On this picture, 1-hexene in run 233 results from equilibration with a pool 

This complicated matter is summarized in the accompanying diagram in which hexane-do.7 represents the average composition of hexane made from the (D ) = 0.35 pool. 

Process 4 ). Desorption of HD must be very slow on the sites of low (D) which lead to processes (1), (5), (7), and (9) in order for (D ) to be so low. On the contrary, process (4 ) must be relatively very fast on sites of high (D) which lead to processes (3) and (8). 

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