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Related Concept Videos

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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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...
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Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

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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...
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[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

3.1K
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
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Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

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The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
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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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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

2.0K
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.
Selection Rules: Photochemical Activation
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Multiple Stimuli-Responsive Conformational Exchanges of Biphen[3]arene Macrocycle.

Yiliang Wang1, Liu-Pan Yang2, Xiang Zhao1

  • 1Center for Supramolecular Chemistry and Catalysis and Department of Chemistry, School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China.

Molecules (Basel, Switzerland)
|December 11, 2020
PubMed
Summary

Synthetic macrocycles can rapidly change shape. Researchers observed two distinct conformations of a tetramethoxyl biphenarene macrocycle (MeBP3) that respond to various stimuli, paving the way for molecular switches.

Keywords:
conformational exchangemacrocyclemultiple stimuli-responsive

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Area of Science:

  • Supramolecular Chemistry
  • Organic Chemistry
  • Materials Science

Background:

  • Synthetic macrocycles exhibit dynamic conformational behavior, often influenced by guest molecules.
  • Studying conformational dynamics in the absence of guests is crucial for understanding intrinsic molecular properties.

Purpose of the Study:

  • To investigate and characterize the stimuli-responsive conformational exchanges of a specific tetramethoxyl biphenarene (MeBP3) macrocycle.
  • To explore the potential of MeBP3 as a building block for molecular switches and responsive materials.

Main Methods:

  • Solid-state structural analysis of MeBP3 conformations.
  • Solution-state characterization using proton Nuclear Magnetic Resonance (1H NMR), carbon Nuclear Magnetic Resonance (13C NMR), and 2D NMR techniques.
  • Investigating responses to external stimuli including solvents, temperature variations, guest binding, and acid/base addition.

Main Results:

  • Two distinct, pre-existing conformations of the MeBP3 macrocycle were identified and structurally characterized in the solid state.
  • Conformational exchange dynamics were confirmed in solution via NMR spectroscopy.
  • The conformational states of MeBP3 were demonstrated to be responsive to changes in solvent, temperature, guest presence, and pH.

Conclusions:

  • The MeBP3 macrocycle exhibits dynamic conformational flexibility and stimuli-responsive behavior.
  • These findings highlight the potential utility of MeBP3 in the design of advanced molecular switches and stimuli-responsive systems.
  • Further research into macrocyclic conformational dynamics can lead to novel functional materials.