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The mechanism of propene elimination from metastable methyleneimmonium ions is discussed. T h e + h t field-free region fragmentations of complete sets of isotopically labelled methyleneimmonium ions (H,C=NR'R': R' = R' = n-C,H, ; R' = R' = i-C,H, ; R' = n-C,H, ; R' = C2H, ; R' = n-C,H, ; R' = CH, ; R' = n-C,H, ;Rz = H) were used to support the mechanism presented. The relative amounts of H/D transferred are quantitatively correlated to two distinct mathematical concepts which allow information to be deduced about influences on reaction pathways that cannot be measured directly. Propene loss from the ions examined proceeds via ioweutral complex intermediates For the di-n-propyl species ratedetermining and H/D distributiondetermining steps are clearly distinct. Whereas the former corresponds to a 1,thydride shift in a 1-propyl cation coordinated to an imine moiety, the latter is equivalent to a proton transfer to the imine occurring from the 2-propyl cation generated by the previous step. For the diisopropyl-substituted ions which directly form the 2-propyl cation-containing complex, the ratedetermining hydride shift vanishes. The Zpropyl cation-containing complex can decompose directly or via an intermediate proton-bridged complex. Competition of these routes is not excluded by the experimental results. Assuming a 2: 1 :3 distribution, a preference for the a-and bmethylene of the initial n-propyl chain as the source of the hydrogen transferred is detected for n-propylimmonium ions containing a second alkyl chain R2. This preference shows a clear dependence on the steric influence of R'. During the transfer step isotopic substitution is found to affect the H/D distribution strongly. For the alternative route of McLafferty rearrangement leading to C,H, loss, specific 7-H transfer is observed.

ZUSAMMENFASSUNGDas Brutpheromon der Honigbiene, Gyceryl-1,2dioleat-3-palmitat, löste

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