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Related Concept Videos

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

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

1.4K
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...
1.4K
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

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

1.8K
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.
1.8K
Conformations of Cyclohexane02:11

Conformations of Cyclohexane

16.7K
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...
16.7K
Conformations of Butane02:20

Conformations of Butane

19.6K
Unlike ethane and propane that have only two major conformations, butane has more than two conformers. The staggered form of butane in which the bulky methyl groups on the two carbons are placed on opposite sides, that is, at a dihedral angle of 180°, is the lowest energy, most stable form — called the anti conformer. This conformation is stabilized due to the absence of steric repulsion between the largely spaced out methyl groups. The other two staggered conformations are...
19.6K
Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

20.3K
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...
20.3K
Conformations of Ethane and Propane02:18

Conformations of Ethane and Propane

18.7K
In an organic molecule, free rotation about the carbon-carbon single bond results in energetically different conformers of the molecule. Due to this rotation, called the internal rotation, ethane has two major conformations — staggered and eclipsed.
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered...
18.7K

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Beyond Rotatable Bond Counts: Capturing 3D Conformational Flexibility in a Single Descriptor.

Jerome G P Wicker1, Richard I Cooper1

  • 1Chemical Crystallography, University of Oxford , Oxford OX1 3TA, U.K.

Journal of Chemical Information and Modeling
|December 28, 2016
PubMed
Summary
This summary is machine-generated.

A novel molecular descriptor, nConf20, quantifies molecular flexibility by assessing accessible conformational space. This new metric significantly improves predictions of molecular crystallization compared to existing methods.

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Area of Science:

  • Computational chemistry
  • Cheminformatics
  • Drug discovery

Background:

  • Molecular flexibility is crucial for predicting crystallization behavior.
  • Existing descriptors like rotatable bond count (RBC) and Kier flexibility index have limitations in capturing conformational space.
  • There is a need for improved molecular descriptors to accurately quantify flexibility.

Purpose of the Study:

  • To introduce a new molecular descriptor, nConf20, that effectively captures a molecule's accessible conformational space.
  • To evaluate the performance of nConf20 in predicting molecular crystallization.
  • To compare nConf20 with existing flexibility descriptors.

Main Methods:

  • Developed nConf20 based on chemical connectivity.
  • Utilized RDKit conformer generator to sample molecular conformational space.
  • Applied nConf20 as a single-variable classifier for crystallization prediction.
  • Integrated nConf20 into rule-based analysis of machine learning models.

Main Results:

  • nConf20 accurately captures the accessible conformational space of molecules.
  • nConf20 significantly outperforms previous single-variable classifiers in predicting crystallization.
  • nConf20 enhances the interpretability of black-box machine learning models for crystallization analysis.

Conclusions:

  • nConf20 is a powerful new descriptor for quantifying molecular flexibility.
  • nConf20 demonstrates superior performance in predicting molecular crystallization.
  • The descriptor offers valuable insights for drug discovery and materials science by improving crystallization prediction.