Related Experiment Video
Updated: Mar 8, 2026
14:55
Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
16.1K
Internal dynamics in helical molecules studied by X-ray diffraction, NMR spectroscopy and DFT calculations
Martin Dračínský1, Jan Storch2, Vladimír Církva2
1Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo 2, 16610 Prague, Czech Republic. dracinsky@uochb.cas.cz.
Physical Chemistry Chemical Physics : PCCP
|January 13, 2017
Summary
[6]helicene exhibits surprising flexibility, with its helical structure expanding at higher temperatures. This conformational change was observed using nuclear magnetic resonance (NMR) and confirmed by computational modeling.
Area of Science:
- Organic chemistry
- Molecular dynamics
- Spectroscopy
Background:
- Helicenes are chiral aromatic hydrocarbons with a unique helical structure.
- Understanding the conformational dynamics of helicenes is crucial for their applications in materials science and asymmetric synthesis.
- Previous studies suggested limited flexibility in [6]helicene, a foundational molecule in this class.
Purpose of the Study:
- To investigate the conformational behavior of [6]helicene and its fluorinated derivatives.
- To explore the relationship between temperature and the molecular structure of helicenes.
- To elucidate the dynamic processes governing helicene conformation in different states.
Main Methods:
- Variable-temperature Nuclear Magnetic Resonance (NMR) spectroscopy (¹H, ¹³C, ¹⁹F).
- Analysis of existing crystal structures of [6]helicene.
- Density Functional Theory (DFT) calculations, including conformational analysis and molecular dynamics simulations.
Main Results:
- Crystal structures revealed unexpected flexibility in the [6]helicene framework.
- NMR experiments showed unusual temperature-dependent chemical shifts for peripheral atoms.
- DFT calculations supported the interpretation of temperature-induced 'pitch' opening of the helicene structure.
Conclusions:
- [6]helicene and its derivatives display significant conformational flexibility, contrary to previous assumptions.
- Elevated temperatures promote an opening of the helical 'pitch', altering molecular geometry.
- The study provides a comprehensive understanding of helicene dynamics through integrated experimental and computational approaches.
Related Concept Videos
00:52¹H 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
01:15¹H 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
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
1.7K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.7K
01:13¹H NMR: Complex Splitting
2.1K
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
2.1K
01:17Spin–Spin Coupling: One-Bond Coupling
1.6K
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
1.6K
02:36Molecular Geometry and Dipole Moments
19.8K
The VSEPR theory can be used to determine the electron pair geometries and molecular structures as follows:
19.8K