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Diels–Alder Reaction: Characteristics of Dienes

Diels–Alder Reaction: Characteristics of Dienes

The Diels–Alder reaction brings together a diene and a dienophile to form a six-membered ring. Both components have unique characteristics that influence the rate of the reaction.
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable, the...

Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry

Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry

Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.

Preparation and Reactions of Sulfides

Preparation and Reactions of Sulfides

Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.

Disubstituted Cyclohexanes: cis-trans Isomerism

Disubstituted Cyclohexanes: cis-trans Isomerism

Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers.

Stability of Conjugated Dienes

Stability of Conjugated Dienes

Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.

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Related Experiment Video

Updated: May 16, 2026

Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

Published on: November 27, 2015

New isolable dialkylsilylene and its isolable dimer that equilibrate in solution.

Takashi Abe¹, Ryoji Tanaka, Shintaro Ishida

¹Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.

Journal of the American Chemical Society

|November 23, 2012

Summary

A novel dialkylsilylene was synthesized and isolated. Its reversible dimerization to a tetraalkyldisilene was observed, with flexible steric bulk enabling the isolation of both silicon species.

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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

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Published on: November 27, 2015

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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Published on: April 19, 2019

Area of Science:

Organosilicon Chemistry
Inorganic Synthesis
Spectroscopy

Background:

Divalent silicon compounds (silylenes) are highly reactive intermediates.
Isolation of stable silylenes requires significant steric protection.
Dimerization of silylenes to disilenes is a common reaction pathway.

Purpose of the Study:

To synthesize and characterize a novel isolable dialkylsilylene.
To investigate the dimerization equilibrium between the silylene and its corresponding disilene.
To understand the role of steric bulk in stabilizing these silicon species.

Main Methods:

Synthesis of dialkylsilylene 3.
Recrystallization to obtain monomeric silylene 3 and dimeric tetraalkyldisilene 4.
Solid-state structural analysis (X-ray crystallography).
Solution-state characterization using NMR and UV-vis spectroscopies.
Thermodynamic analysis of the silylene-disilene equilibrium.

Main Results:

Successful synthesis and isolation of dialkylsilylene 3.
Isolation of tetraalkyldisilene 4, a dimer of 3, with a long Si=Si bond (2.252 Å).
Observation of a reversible equilibrium between silylene 3 and disilene 4 in solution.
Quantification of thermodynamic parameters for the dimerization equilibrium (ΔH = -36 ± 3 kJ mol⁻¹, ΔS = -170 ± 15 J mol⁻¹ K⁻¹).
Analysis of steric factors (percent buried volume) explaining the stability and isolation of both species.

Conclusions:

The flexible steric bulk of the alkyl substituent is crucial for the reversible dimerization and isolation of both silylene and disilene.
This study provides insights into the factors controlling the stability and reactivity of low-valent silicon compounds.
The findings contribute to the understanding of silicon-silicon multiple bond formation and stabilization.