1,2-Propanediol pinacol rearrangement

The pinacol rearrangement is frequently observed when geminal diols react with acid. The stmcture of the products from unsymmetrical diols can be predicted on the basis of ease of carbocation formation. For example, l,l-diphenyl-2-metltyl-l,2-propanediol rearranges to... 

Problem 14.37 Give the structural formula for the major product from the pinacol rearrangement of 1,1,2-triphenyl-1,2-propanediol. Indicate the protonated OH and the migrating group <... 

Problem 14.59 Outline the steps and give the product of pinacol rearrangement of (a) 3-phenyl-l,2-propanediol, (b) 2,3-diphenyl-2,3-butanediol. ... 

J. F. Duncan and K. R. Lynn, J. Chem. Soc., 3512, 3519 (1956) J. B. Ley and C. A. Vernon, Chem. Ini. (London), 146 (1956).] That the rate-determining step can be the migration when the first-formed carbocation is particularly stable has been shown by Schubert and LeFevre [note 18(b)]. These workers subjected 1,1-diphenyl-2-methyl- 1,2-propanediol to the pinacol rearrangement and found that deuterium substitution in the migrating methyls caused the reaction to slow down. 

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