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Stability of Conjugated Dienes01:28

Stability of Conjugated Dienes

3.3K
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.
3.3K
Stereoisomerism of Cyclic Compounds02:33

Stereoisomerism of Cyclic Compounds

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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,...
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π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

1.1K
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
1.1K
Structure of Conjugated Dienes01:16

Structure of Conjugated Dienes

4.9K
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...
4.9K
π Molecular Orbitals of 1,3-Butadiene01:24

π Molecular Orbitals of 1,3-Butadiene

8.8K
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...
8.8K
Conformations of Cyclohexane02:11

Conformations of Cyclohexane

12.2K
Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
12.2K

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Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives
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Spring-Like Behavior in [8]Helicene Diimides: How Helical Pitch Governs Optical Anisotropy and Electronic

Fridolin Saal1, Vincenzo Brancaccio1, Krzysztof Radacki2

  • 1Institut für Organische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany.

Angewandte Chemie (International Ed. in English)
|June 13, 2025
PubMed
Summary

Researchers engineered [8]helicene diimides ([8]HDIs) with tunable helical pitches. This precise structural control enhances optical properties and electronic communication for advanced chiral materials.

Keywords:
Chiroptical spectroscopyHelical structuresHelicenesMolecular springOptical anisotropy

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Supramolecular Chemistry

Background:

  • Helicenes are molecular springs with corkscrew geometry, useful for chiral materials.
  • Precise structural modulation is key to engineering their functional properties.

Purpose of the Study:

  • To design and synthesize [8]helicene diimides ([8]HDIs).
  • To demonstrate tunable helical pitch via alkyl chain bridging.
  • To investigate the impact of helical pitch on optical and electronic properties.

Main Methods:

  • Synthesis of [8]helicene diimides with varying alkyl chain lengths (C3-C6).
  • Spectroscopic and chiroptical measurements.
  • X-ray crystallography.
  • Quantum chemical calculations.

Main Results:

  • Precisely tunable helical pitch in [8]HDIs.
  • High optical dissymmetry factors (up to 6.0 × 10-2).
  • Enhanced through-space conjugation.
  • Controlled crystal packing in enantiopure and racemic samples.

Conclusions:

  • Alkyl chain length effectively tunes helical pitch and properties of [8]HDIs.
  • This strategy enables systematic control over optical anisotropy and electronic communication.
  • The findings offer a pathway for designing advanced chiral functional materials.