Transition structures medium-sized rings

The rearrangement of [13] bears a close resemblance to the transannular reactions observed in medium sized rings that have been reviewed by Prelog and Traynham (1963) and Cope et al. (1966). Recently Sorensen and coworkers have studied medium sized cycloalkyl cations under stable ion conditions in non-nucleophilic media and demonstrated that their structures are ji.-hydrido-bridged. The bonding situation in these ions contrasts sharply with that in the ions described above and rather corresponds to that of transition states (or intermediates) for intramolecular hydride transfer in these ions. 

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