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Related Concept Videos

Structure of Conjugated Dienes01:16

Structure of Conjugated Dienes

Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
Stability of Conjugated Dienes01:28

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.
Stereoisomerism of Cyclic Compounds02:33

Stereoisomerism of Cyclic Compounds

In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
π Molecular Orbitals of 1,3-Butadiene01:24

π Molecular Orbitals of 1,3-Butadiene

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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Updated: Jun 24, 2026

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
06:55

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

Published on: September 26, 2016

Exploring 2-D σ-σ* Conjugation in Cyclic Polysiloxane Copolymers.

Zijing Zhang1, Cecilia Pilon2, Pimjai Pimbaotham3

  • 1Dept. of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, USA.

Macromolecular Rapid Communications
|June 23, 2026
PubMed
Summary

This study defines unconventional conjugation across silicon-oxygen-silicon bonds in novel copolymers. Researchers demonstrate accessible synthesis routes and evidence for sigma-sigma* conjugation, paving the way for new conjugated materials.

Keywords:
conjugated systemcopolymerelectron transferexcited stateheck reactionphotochemistrypolymerpolymer chemistrysubstituentthiophene

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Published on: February 7, 2017

Area of Science:

  • Materials Science
  • Polymer Chemistry
  • Organic Electronics

Background:

  • Unconventional conjugation phenomena across Si─O─Si bonds were previously ill-defined.
  • Need for general synthetic routes to Si─O─Si containing copolymers with tunable electronic properties.

Purpose of the Study:

  • To clearly define and elucidate the mechanisms of conjugation across Si─O─Si bonds.
  • To provide accessible synthetic routes to novel Si─O─Si containing copolymers.
  • To investigate the photophysical properties and conjugation extent in these new materials.

Main Methods:

  • Synthesis of 1:1 Vy₄D₄:Ar copolymers using Heck catalytic cross-coupling.
  • Characterization of optical absorption and emission properties.
  • Investigation of electronic interactions using F₄TCNQ (tetracyanoquinodimethane) and theoretical modeling.

Main Results:

  • Synthesized copolymers exhibit characteristic absorption and red-shifted emission attributed to σ-σ* transitions.
  • Substituent-dependent modulation of photophysics, with thiophene co-monomers yielding lowest-energy excited states.
  • Evidence for σ-σ* conjugation in both undecorated and decorated copolymers, and even in substituted cyclomers.
  • Theoretical modeling suggests significant flattening of cyclomers in the excited state, indicating potential for 2-D conjugation.

Conclusions:

  • Established clear definitions and mechanisms for Si─O─Si bond conjugation.
  • Demonstrated facile synthesis of novel σ-σ* conjugated copolymers and cyclomers.
  • Highlighted the potential for 2-D conjugation in decorated systems and raised questions about excited-state ring currents.