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Preparation of Epoxides03:00

Preparation of Epoxides

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Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
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Structure and Nomenclature of Epoxides02:38

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Cyclic ethers are heterocyclic compounds with an oxygen atom in the ring along with carbon atoms. They are named depending on the number of carbon atoms present in their ring system. Cyclic ethers with a three-membered ring system are called “oxirane”, four-membered ring systems as “oxetane”, five-membered ring systems as “oxolane”, and six-membered ring systems as “oxane”. The cyclic structure of these rings imposes angle strain, and this strain...
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Acid-Catalyzed Ring-Opening of Epoxides02:24

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Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
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Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control01:23

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The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.
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π Molecular Orbitals of 1,3-Butadiene01:24

π Molecular Orbitals of 1,3-Butadiene

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Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
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The electrophilic addition of hydrogen halides such as HBr to alkenes and nonconjugated dienes gives a single product as per Markovnikov’s rule.
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Configurational Assignment of Epoxides Using HMBC: DFT-Based Development, Experimental Validation, Scope, and

Ryuhi Kanehara1, Kako Shirakawa2, Hayato Sakashita2

  • 1The United Graduate School of Agricultural Science, Iwate University, 18-8 Ueda 3 Chome, Morioka, Iwate 020-8550, Japan.

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Summary
This summary is machine-generated.

This study introduces a new method for determining epoxide configurations using density functional theory calculations and HMBC signal intensities. The approach correlates epoxide conformation with NMR data, successfully assigning configurations for most tested epoxides.

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Area of Science:

  • Organic Chemistry
  • Computational Chemistry
  • Spectroscopy

Background:

  • Configurational assignment of epoxides is difficult due to their quasi-planar structure.
  • Existing methods may lack efficiency or applicability for certain epoxide types.

Purpose of the Study:

  • To develop a reliable protocol for predicting epoxide configurations.
  • To utilize density functional theory (DFT) calculations and Heteronuclear Multiple Bond Correlation (HMBC) spectroscopy for this purpose.

Main Methods:

  • DFT calculations of nJCH coupling constants.
  • Correlation of epoxide conformation (dihedral angles) with HMBC signal intensities.
  • Analysis of conformational sectors (synperiplanar, synclinal, anticlinal, antiperiplanar).

Main Results:

  • Developed a protocol correlating epoxide conformation and HMBC signals for configuration prediction.
  • 2JCH and 3JCH values showed predictable patterns based on dihedral angles.
  • Successfully assigned configurations for 14 out of 15 tested epoxides, demonstrating high reliability and generality.

Conclusions:

  • The developed protocol provides an effective means for epoxide configurational assignment.
  • The method is generally applicable to ring epoxides, with minor adjustments for boundary conformational regions.