Pinacol/pinacolone rearrangement migratory aptitude

Chang, C.K. and Sotiriou, C.., Migratory aptitudes in pinacol-pinacolone rearrangement of vic-dihydroxychlorins, /. Heterocyclic Chem., 22,1739,1985, and references therein. 

A number of experiments have been carried out to determine the relative migratory aptitude of groups in pinacol/pinacolone type rearrangements, and in general the relative ease of migration is found to be ... 

Of the two OH groups, the one which forms the more stable carbocation is protonated preferentially. This factor takes precedence over the migratory aptitude factor. Further evidence for carbenium ion formation in the pinacol rearrangement has been obtained by oxygen-exchange experiments. Partial rearrangement of pinacol to pinacolone has been carried out in acidic solutions containing H20 (Scheme 2.27). 

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