Hydrogen as a migrating group in some pinacol ­rearrangements: a DFT study

Abstract

DFT calculations at the Becke3LYP/6-31G* level were employed to demonstrate that the pinacol rearrangement of ethylene glycol and the 1,1-dimethyl and 1,1,2-trimethyl analogs undergo pinacol rearrangements by a concerted hydrogen-bridged transition structure. No evidence for a bridged intermediate was found. Calculations by two methods on the ethylene glycol system were repeated with the various structures embedded in a solvent cavity with the medium dielectric constant set for water. The ratio of rates for the two methylated glycols was calculated with good agreement with the experimental value. The kinetic isotope effect for the rearrangement of 1,1,2-trimethylethylene glycol was calculated (2.8) in fair agreement with the experimental value of 1.6. Sources of error are briefly discussed.

Divergent Reactivity during the Trapping of Benzynes by Glycidol Analogs: Ring Cleavage via Pinacol-Like Rearrangements vs Oxirane Fragmentations

“…4% of 7- d 1 , small amounts of the isomeric monodeuterated products 8- d 1 and 8- d 1 ′ (Figure c) were also detected in the 1 H NMR spectrum of the sample of aldehyde 8- d 2 produced in this experiment. Qualitatively there was a greater amount of 8- d 1 than 8- d 1 ′ formed, as would be expected from a normal kinetic isotope effect associated with the product-determining, 1,2-hydride shift . Partial overlap of key resonances in the 1 H NMR spectrum (see Supporting Information) precluded an accurate, quantitative determination of the actual 8- d 1 : 8- d 1 ′ product ratio.…”

“…(b) A deuterium-labeling experiment that supports a pinacol-like mechanism. (c) The greater amount of isomeric monodeuterated product 8- d 1 compared to 8- d 1 ′ is consistent with preferential migration of protide vs deuteride …”

Reaction pathway of aliphatic pinacol‐type rearrangement reexamined

“…Relative rates of 18 O exchange and loss of optical activities versus rearrangement were consistent with the stepwise ionization‐migration mechanism. In gas‐phase experiments, a concerted ionization‐migration mechanism was demonstrated,21–23 which was supported by computational studies at the HF24, 25 and the DFT level 26, 27. As in the cases of aromatic systems, an OH migration was observed under strong acidic conditions, but a possible role of epoxide in aliphatic pinacol rearrangement was not clarified.…”

Advances and Perspectives in Pinacol Rearrangement Reactions: A Comprehensive Review

“…Pinacol rearrangement is a well-known organic reaction that involves the conversion of a pinacol (a type of diol) into a carbonyl compound through the migration of a functional group. In this study, the author, William Smith, employs computational modeling to explore the feasibility and mechanistic aspects of hydrogen migration in pinacol rearrangements [16]. The research begins by selecting specific pinacol substrates with hydrogen atoms in strategic positions for potential migration.…”