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Related Concept Videos

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
Properties of Enantiomers and Optical Activity02:24

Properties of Enantiomers and Optical Activity

It is essential to understand the difference between chiral and achiral interactions and the implications thereof in optical activity and their applications. Just as our feet, which are chiral, interact uniquely with chiral objects, such as a pair of shoes, but identically with achiral socks, enantiomers of a molecule exhibit different properties only when they interact with other chiral media. An example of a significant implication from this facet is the phenomenon known as optical activity,...
Chirality at Nitrogen, Phosphorus, and Sulfur02:30

Chirality at Nitrogen, Phosphorus, and Sulfur

Chirality is most prevalent in carbon-based tetrahedral compounds, but this important facet of molecular symmetry extends to sp3-hybridized nitrogen, phosphorus and sulfur centers, including trivalent molecules with lone pairs. Here, the lone pair behaves as a functional group in addition to the other three substituents to form an analogous tetrahedral center that can be chiral.
A consequence of chirality is the need for enantiomeric resolution. While this is theoretically possible for all...
Phase Transitions: Melting and Freezing02:39

Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
Phase Transitions02:31

Phase Transitions

Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to occupy...

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Related Experiment Video

Updated: Jun 14, 2026

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
06:24

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Published on: October 31, 2019

Low temperature enantiotropic nematic phases from V-shaped, shape-persistent molecules.

Matthias Lehmann1, Jens Seltmann

  • 1Institute of Chemistry, Chemnitz University of Technology, Strasse der Nationen 62, 09111 Chemnitz, Germany. Matthias.Lehmann@chemie.tu-chemnitz.de

Beilstein Journal of Organic Chemistry
|March 20, 2010
PubMed
Summary

Researchers developed V-shaped thiadiazole liquid crystals with improved mesophase properties. Optimizing spacer lengths enhanced the nematic phase range and lowered melting points for these shape-persistent molecules.

Keywords:
V-shaped mesogensbiaxial nematicsliquid crystalsphase engineeringthiadiazoles

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Published on: May 15, 2017

Area of Science:

  • Materials Science
  • Organic Chemistry
  • Liquid Crystals

Background:

  • Thiadiazole nematogens are organic compounds exhibiting liquid crystalline properties.
  • Oligo(phenylene ethynylene) scaffolds offer structural rigidity for shape-persistent molecules.
  • Alkyloxy spacers and ester groups influence mesophase behavior.

Purpose of the Study:

  • To synthesize and characterize novel V-shaped thiadiazole nematogens.
  • To investigate the effect of desymmetrized alkyloxy spacers on mesophase properties.
  • To understand the molecular alignment in magnetic fields.

Main Methods:

  • Two-step synthesis of thiadiazole nematogens.
  • Phase behavior analysis through temperature-dependent optical microscopy and differential scanning calorimetry.
  • Optical investigations using conoscopy.
  • X-ray diffraction studies on magnetically aligned samples.

Main Results:

  • Efficient synthesis of V-shaped, shape-persistent thiadiazole nematogens.
  • Optimized mesophase range and low melting temperature achieved with butoxy and heptyloxy spacers.
  • Enantiotropic nematic mesophases observed over a wide temperature range (ΔT = 150° C).
  • Uniaxial nematic phase confirmed by conoscopy.
  • X-ray studies revealed specific molecular alignment patterns in magnetic fields.

Conclusions:

  • Desymmetrization of spacers is crucial for optimizing liquid crystal properties.
  • The V-shaped thiadiazole nematogens exhibit excellent nematic phase behavior.
  • Molecular self-assembly in magnetic fields follows predictable patterns for these V-shaped molecules.