Name: pinacol coupling and solvent effects
Uploaded: 2023-04-30T11:22:57.000Z
Duration: 1 min 27 s
Channel: JoVE

Pinacol bağlanması, radikal bir dimerizasyon reaksiyonudur ve aldehitlerin veya ketonların bir hidrokarbon çözücü içinde indirgeyici olarak bağlanmasını içerir.
Bir metalden keton gibi spin eşleştirilmiş bir moleküle tek bir elektron transferi, reaksiyonu başlatır ve bir ketil - radikal bir anyon oluşturur. Ketil, karbon veya oksijen üzerindeki radikal ve diğer üzerindeki yük ile temsil edilebilir.
Burada sodyum ve magnezyum gibi metaller bir elektron kaynağı görevi görür.
Ketilin kaderi, reaksiyon için kullanılan çözücüye bağlıdır.
Etanol gibi protik çözücülerde, ketil protonlanır, ardından asitleşme üzerine alkol oluşturan bir alkoksit anyonu vermek için ikinci bir elektron transferi yapılır.
Bununla birlikte, benzen gibi aprotik çözücülerde, protonların yokluğu ketil birikimine izin verir ve bu da bir dirol içine dimerizasyonuna yol açar. Bu, pinacol bağlantısının temelini oluşturur.
Özellikle, negatif yükler arasındaki elektrostatik itme, dimerizasyonu engellemez, çünkü magnezyum gibi metaller kovalent metal-oksijen bağları oluşturarak ketillere koordine olur ve hızlı tepki vermelerini sağlar.

aldehitlerin veya ketonların İndirgeyici bağlanması yoluyla vicinal dioller: pinacol bağlanmasına genel bakış

Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview

Wilhelm Rudolph Fittig, pinacol birleştirme reaksiyonunu 1859'da keşfetti. Bu, radikal bir dimerizasyon reaksiyonudur ve komşu dioller vermek üzere hidrokarbon solventi varlığında aldehitlerin veya ketonların indirgeyici bağlanmasını içerir.

<img alt="Figure1" src="/files/ftp_upload/12905/12905_PT_Figure_1.svg" style="text-align: center; height: 160px;">

Radikal reaksiyon, bir radikal anyon olan bir ketil oluşturmak üzere sodyum ve magnezyum gibi metallerden aldehitler veya ketonlar gibi spin çiftli bir moleküle tek bir elektron transferi ile başlatılır. Ketil, karbon atomunda radikal bir karaktere ve oksijen atomunda bir yüke sahiptir. Rezonans formu, oksijen atomu üzerinde konumlandırılmış bir radikale ve karbon atomu üzerinde bir yüke sahiptir.

Ketil davranışı, reaksiyonun gerçekleştirildiği çözücüden büyük ölçüde etkilenir.

Etanol gibi protik çözücüler ketili protonlaştırır. Bunu, bir alkoksit anyonu vermek üzere metalden ikinci bir elektron transferi takip eder. Ayrıca bir alkoksit anyonunun asitleştirilmesi alkol oluşturur. Burada metal reaksiyonla birlikte çözünür ve serbest elektron kaynağı görevi görür.

Benzen veya eter gibi aprotik çözücülerin varlığında ketil radikal anyonları, protonların yokluğundan dolayı protonasyona uğramazlar. Bu, ketil dimerizasyonunu teşvik eder ve ünlü pinakol birleştirme reaksiyonunun bir parçasını oluşturur.

İlginç bir şekilde, magnezyum, alüminyum veya sodyum gibi metaller, birkaç ketil radikaliyle koordine olan ve bir diol oluşturmak üzere hızla reaksiyona giren kovalent metal-oksijen bağları oluşturarak reaksiyonu kolaylaştırır. Özellikle ketillerin negatif yükleri arasındaki elektrostatik itmeler dimerizasyonu engellemez. Özetle, protik çözücüler alkol oluşumunu desteklerken, aprotik çözücüler komşu diolleri destekler.

Aldehitlerin veya Ketonların İndirgeyici Bağlanması Yoluyla Vicinal Dioller: Pinacol Bağlanmasına Genel Bakış

Wilhelm Rudolph Fittig, 1859'da pinacol eşleşme reaksiyonunu keşfetti. Radikal bir dimerizasyon reaksiyonudur ve indirgeyici bir şekilde birleştirilmesini içerir ...

vicinal-diols-via-reductive-coupling-aldehydes-or-ketones-pinacol

Education

JoVE Core

Organic Chemistry

Organik Kimya

Unit 1

Ünite 1

Radical Chemistry

Radikal Kimya

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

pinacol coupling and solvent effects

Pinacol coupling is a radical dimerization reaction that joins aldehydes or ketones to form vicinal diols. Wilhelm Rudolph Fittig first discovered this reaction in 1859. It is a reductive coupling, which means the molecules are joined after they gain electrons.

The reaction begins with a single electron transfer from metals such as sodium or magnesium to an aldehyde or ketone. This forms a ketyl, a radical anion. In a ketyl, the carbon atom can carry radical character while the oxygen atom carries a negative charge. A resonance form also places the radical on oxygen and the charge on carbon.

The solvent has a major effect on the outcome. In protic solvents, such as ethanol, the ketyl is protonated first. A second electron transfer from the metal then gives an alkoxide anion. After acidification, this alkoxide forms an alcohol. In this way, the metal acts as a source of free electrons as it dissolves during the reaction.

In aprotic solvents, such as benzene or ether, protonation does not occur because there are no protons available. This favors ketyl dimerization and leads to pinacol coupling. Metals such as magnesium, aluminum, or sodium can help by forming covalent metal-oxygen bonds that coordinate several ketyl radicals. Even though the ketyls carry negative charge, electrostatic repulsion does not stop them from dimerizing. As a result, aprotic solvents favor vicinal diols, while protic solvents favor alcohol formation.

Pinacol Coupling and Solvent Effects

radicals: electronic structure and geometry

radicals-electronic-structure-and-geometry

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Radical geometry depends on the electronic structure around the radical center. An unpaired electron, like a lone pair, affects the shape of the molecule. For a trivalent radical, the structure falls between the geometries of carbocations and carbanions. A carbocation with sp2 hybridization is trigonal planar. A carbanion with sp3 hybridization is trigonal pyramidal. The difference comes from the number of nonbonding electrons. The carbocation has none, while the carbanion has two. A carbon...

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EPR Hyperfine Splitting in Organic Radicals

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Radical abstraction helps drive radical chain reactions. In this process, a relatively unstable radical removes an atom from a compound and forms a new radical that is more stable. The atom taken in this step can be hydrogen or a halogen. A radical initiator can first form radicals by homolysis, which is the breaking of a spin-paired molecule into two radicals. That is different from abstraction. In abstraction, a radical reacts with a spin-paired molecule and produces one new radical plus one...

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Allylic Chlorination by Radical Chain Reaction

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HBr Selectivity in Alkene Addition Thermodynamics

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vicinal diols via reductive coupling of aldehydes or ketones: pinacol coupling overview

Pinacol coupling is a radical dimerization reaction that joins aldehydes or ketones to form vicinal diols. Wilhelm Rudolph Fittig first discovered this reaction in 1859. It is a reductive coupling, which means the molecules are joined after they gain electrons. The reaction begins with a single electron transfer from metals such as sodium or magnesium to an aldehyde or ketone. This forms a ketyl, a radical anion. In a ketyl, the carbon atom can carry radical character while the oxygen atom...

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Titanium-Coupled Alkenes from Carbonyls

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key terms and concepts

Learn how pinacol coupling joins aldehydes and ketones into vicinal diols, and how protic versus aprotic solvents change the product.

Pinacol Coupling and Solvent Effects | JoVE K12

organic chemistry

JoVE Core Organik Kimya, kısa ve anlaşılması kolay animasyonlu video dersleri kullanarak stereokimya, reaksiyonlar ve mekanizmaların temel kavramlarını açıklar. Buna ek olarak, bilim insanlarının yer aldığı videolar, ilgili kavramların günümüz laboratuvarlarında gerçekleştirilen klasik ve orijinal araştırma deneylerinde nasıl uygulandığını göstermektedir.

Pinacol Coupling and Solvent Effects

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