Hydrogen shift, distant

Shifts to Distant Carbons Although there are many examples of 1,2-hydrogen and alkyl shifts, the occurrence of 1,3, 1,4, and 1,5 shifts must also be considered. A sequence of 1,2 shifts, however, can often yield the same results as a 1,3 or 1,4 shift, and the unambiguous demonstration of such can be difficult. 

According to the rules of orbital symmetry, vicinal hydride shift in cations is a thermally allowed suprafacial 1,2-sigmatropic shift. Migration of a more distant hydrogen can occur by successive 1,2-shifts, via a bridged structure (such as the cyclooctyl cation in Scheme 7 ), or by corner-to-corner transfer in a protonated cyclopropane (which give net 1,3-shifts). An EBFlow experiment has been able to measure the competition between 1,2- and 1,3-shift in the 1-fluoropropyl system. 

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