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Related Concept Videos

Prochirality02:05

Prochirality

The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
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Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
Thermal Electrocyclic Reactions: Stereochemistry01:17

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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
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Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Molecules with Multiple Chiral Centers02:25

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Molecules that possess multiple chiral centers can afford a large number of stereoisomers. For instance, while some molecules like 2-butanol have one chiral center, defined as a tetrahedral carbon atom with four different substituents attached, several molecules like butane-2,3-diol have multiple chiral centers. A simple formula to predict the number of stereoisomers possible for a molecule with n chiral centers is 2n. However, there can be a lower number where some of the stereoisomers are...
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,...

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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
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Dual-Stimulus Chiroptical Switch of Tetrastable [3]Rotaxanes.

Xinhui Fan1, Yubing Gong1, Zhicheng Guan2

  • 1College of Science, Henan Agricultural University, Zhengzhou 450002, China.

Organic Letters
|June 9, 2026
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Summary

Researchers created chiral rotaxanes that change color with light and acid/base stimuli. These molecules exhibit tunable photochromism and can induce chirality in achiral components through mechanical motion.

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Area of Science:

  • Supramolecular Chemistry
  • Materials Science
  • Organic Chemistry

Background:

  • Rotaxanes are mechanically interlocked molecules with potential applications in molecular machines.
  • Photochromic materials change color upon light exposure, offering possibilities for optical data storage and sensors.
  • Chirality, or 'handedness,' is crucial in biological systems and asymmetric synthesis.

Purpose of the Study:

  • To construct novel dual-stimulus-responsive chiral tetrastable [3]rotaxanes.
  • To investigate the tunable photochromic properties driven by mechanical motion.
  • To explore the induction and modulation of chirality in achiral units within the rotaxane system.

Main Methods:

  • Synthesis of rotaxanes using a threading-stoppering-methylating strategy.
  • Characterization of photochromic behavior under different stimuli (acid-base, light).
  • Analysis of mechanical motions and their influence on molecular chirality.

Main Results:

  • Successfully synthesized dual-stimulus-induced movable enantiomeric chiral tetrastable [3]rotaxanes.
  • Demonstrated tunable photochromic properties linked to acid-base-driven macrocycle movement on a dithienylethene (DTE) unit.
  • Achieved light- and acid-base-induced chirality in the DTE segment through conformational confinement by chiral macrocycles.

Conclusions:

  • The developed rotaxanes exhibit controllable photochromism and mechanical motion.
  • Chirality can be dynamically induced and modulated in achiral components via supramolecular interactions.
  • These findings open avenues for designing sophisticated molecular switches and chiroptical materials.