18 Mar pinacol–pinacolone rearrangement. methyl migration. pyridinyl migration. The pinacol rearrangement is a well-known reaction in which a glycol. 15 Mar Pinacol-pinacolone rearrangements. Mechanism ♢ Mechanism of the pinacol rearrangement of a symmetrical glycol CH3 CH3 CH3 CH3 _. 10 Oct Pinacol-Pinacolone rearrangement over solids supported metal ion catalysts. Article (PDF Available) in Indian Journal of Chemical Technology.
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In an publication Wilhelm Rudolph Fittig described the reaction of acetone with potassium metal Your question is essentially why the C-C bond migrates instead of the C-H bond, right? You immediately form the aldehyde after ring contraction. In these reactions, the stereochemistry of the diol plays a crucial role in deciding the major product. There just don’t seem piancol be as many interesting organic questions these days.
Rearrangement of this isomer can only produce the cyclopentyl derivative. As it stands, your answer seems claiming something without proving it. In an equilibrium mixture of these isomers we would expect the equatorial, equatorial isomer to predominate because both hydroxyl groups are in the sterically less encumbered equatorial position and both hydroxyls can hydrogen bond with each other in this conformation.
Such migrations have a strong preference for occurring by way of an anti-periplanar geometry. Pinacooone reactions run in strong acid are never clean. This answer implies a concerted mechanism, while the mechanism is usually written stepwise.
But in pinacollne case, when there is a H shift possible, why does it not happen? In the course of this organic reactionprotonation of one of the —OH groups occurs and a carbocation is formed. NilayGhosh in that question about stereochemistry is not mentioned. Ring contraction in pinnacolone rearrangement of cyclohexane-1,2-diol.
Again Fittig was unable to assign a molecular structure to the reaction product which he assumed to be another isomer or a polymer. This is perhaps the best explanation available- chemistry. Shouldn’t the intermediate carbocation be stable in a six membered ring rather than a five membered ring? Annalen der Chemie und Pharmacie.
It could be equilibrium driven.
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I forgot that the six membered ring would be puckered rearrangsment not planar. Butlerov theory allowed the structure of carbon atoms in the molecule to rearrange and with this concept a structure for pinacolone could be found.
Sign up using Facebook. If both the —OH groups are not alike, then the one which yields a more stable carbocation participates in the reaction.
Sign up using Facebook. In other projects Wikimedia Commons. I was reading the topic alcohol in that I saw a reaction Pinacol pinacolone rearrangement.