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Related Concept Videos

Molecular Shapes01:18

Molecular Shapes

Molecules have characteristic shapes that are crucial for their function. The arrangement of various electron groups around the central atom dictates their molecular geometry. Electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions between the electron pairs by maximizing the distance between them. The valence electrons form either bonding pairs, located primarily between bonded atoms, or lone pairs.Two regions of electron density in a diatomic...
Molecular Shape and Polarity03:37

Molecular Shape and Polarity

Dipole Moment of a Molecule
Molecular Geometry and Dipole Moments02:36

Molecular Geometry and Dipole Moments

The VSEPR theory can be used to determine the electron pair geometries and molecular structures as follows:
Fischer Projections02:18

Fischer Projections

Learning to draw Fischer projections of molecules and understanding their relevance plays a crucial role in the visual depiction of organic molecules. A Fischer projection is a two-dimensional projection on a planar surface to simplify the three-dimensional wedge–dash representation of molecules. This is especially helpful in the case of molecules with multiple chiral centers that can be difficult to draw. Here, all the bonds of interest are represented as horizontal or vertical lines. While...
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...
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.

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Related Experiment Video

Updated: Jun 21, 2026

Flexural Rigidity Measurements of Biopolymers Using Gliding Assays
07:55

Flexural Rigidity Measurements of Biopolymers Using Gliding Assays

Published on: November 9, 2012

Determining absolute configuration in flexible molecules: a case study.

K M Specht1, J Nam, D M Ho

  • 1Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.

Journal of the American Chemical Society
|September 13, 2001
PubMed
Summary
This summary is machine-generated.

Assigning molecular absolute configuration is difficult, especially for flexible molecules. Combining molecular modeling, NMR, and X-ray crystallography highlights these challenges, with optical rotatory dispersion (ORD) proving most effective for assignment.

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Last Updated: Jun 21, 2026

Flexural Rigidity Measurements of Biopolymers Using Gliding Assays
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Area of Science:

  • Organic Chemistry
  • Stereochemistry
  • Computational Chemistry

Background:

  • Assigning the absolute configuration of molecules is a persistent challenge in chemistry.
  • Conformationally flexible systems present particular difficulties for stereochemical determination, even for experienced researchers.

Purpose of the Study:

  • To illustrate the difficulties in assigning absolute configuration using only solution-based methods.
  • To present a case study employing multiple techniques to determine molecular configuration.
  • To identify the most effective method for absolute configuration assignment in complex systems.

Main Methods:

  • Utilized a combination of molecular modeling and experimental techniques.
  • Employed solution Nuclear Magnetic Resonance (NMR) spectroscopy.
  • Incorporated X-ray crystallography for structural analysis.
  • Calculated and experimentally measured optical rotatory dispersion (ORD) data.

Main Results:

  • Demonstrated the limitations of relying solely on solution-state methods for configuration assignment.
  • X-ray crystallography provided definitive structural information.
  • Comparison of calculated and experimental ORD data offered the most direct route to assigning absolute configuration.

Conclusions:

  • Determining absolute configuration in flexible molecules requires a multi-technique approach.
  • Solution NMR and X-ray crystallography, while valuable, have limitations for this specific task.
  • Optical rotatory dispersion (ORD) analysis, when combined with computational methods, provides a robust solution for assigning absolute configuration.