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Related Concept Videos

Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

14.9K
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.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
14.9K
Conformations of Cyclohexane02:11

Conformations of Cyclohexane

12.8K
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...
12.8K
Conformations of Cycloalkanes02:29

Conformations of Cycloalkanes

12.0K
Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3  hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that...
12.0K
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

906
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...
906
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

2.9K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
2.9K
Newman Projections02:06

Newman Projections

17.3K
Different notations are used to represent the three-dimensional structure of molecules on two-dimensional surfaces. One of the most commonly used representations is the dash-wedge formula. The dashed wedges, solid wedges, and the plane lines indicate the groups situated behind the plane, coming out of the plane, and in the plane, respectively.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as...
17.3K

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Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
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Torsional disorder and planarization dynamics: 9,10-bis(phenylethynyl)anthracene as a case study.

Ina Fureraj1, Darya S Budkina1, Eric Vauthey1

  • 1Department of Physical Chemistry, University of Geneva, 30 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland. eric.vauthey@unige.ch.

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Summary

Torsional disorder in conjugated molecules impacts excited-state dynamics. Planarization occurs via inertial motion for excited states but diffusion for ground states, influenced by potential steepness.

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Area of Science:

  • Photochemistry
  • Molecular Dynamics
  • Spectroscopy

Background:

  • Conjugated molecules with phenylethynyl units exhibit torsional disorder at room temperature.
  • Excited states are more rigid due to conjugation, leading to asymmetric absorption and emission spectra.

Purpose of the Study:

  • Investigate the effect of torsional disorder on excited-state dynamics.
  • Analyze 9,10-bis(phenylethynyl)anthracene in various solvents and polymers.
  • Utilize stationary and ultrafast electronic spectroscopies.

Main Methods:

  • Temperature-dependent absorption spectroscopy.
  • Ultrafast spectroscopy with varying excitation wavelengths.
  • Viscosity and polymer matrix studies.

Main Results:

  • Absorption spectra show inhomogeneous broadening at room temperature.
  • Excitation of planar molecules leads to ground-state re-equilibration.
  • Excitation of disordered molecules induces planarization via viscosity-independent inertial motion.
  • Ground-state dynamics are purely diffusive.

Conclusions:

  • Excited-state dynamics differ significantly from ground-state dynamics.
  • The steepness of the potential energy surface along the torsional coordinate governs this dissimilarity.
  • Torsional disorder plays a crucial role in molecular excited-state behavior.