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Related Concept Videos

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: Complex Splitting01:13

¹H NMR: Complex Splitting

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 first.
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.
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
¹H NMR: Pople Notation01:09

¹H NMR: Pople Notation

The Pople nomenclature system classifies spin systems based on the difference between their chemical shifts. Coupled spins are denoted by capital letters with subscripts indicating the number of equivalent nuclei. When the coupled nuclei have well-separated chemical shifts, they are assigned letters that are far apart in the alphabet, such as A and X. When the difference in chemical shifts is small, coupled nuclei are named using adjacent letters of the alphabet (AB, MN, or XY).
A proton...
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.

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Related Experiment Video

Updated: Jun 17, 2026

MALDI-ToF MS Method for the Characterization of Synthetic Polymers with Varying Dispersity and End Groups
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MALDI-ToF MS Method for the Characterization of Synthetic Polymers with Varying Dispersity and End Groups

Published on: October 3, 2025

The form factor of H-comb polymers.

Steven Zweier, Marvin Bishop

    The Journal of Chemical Physics
    |December 23, 2009
    PubMed
    Summary

    Monte Carlo simulations reveal that ideal H-comb polymers exhibit consistent form factors regardless of size. These findings align well with theoretical predictions for polymer physics.

    Area of Science:

    • Polymer Physics
    • Computational Chemistry
    • Statistical Mechanics

    Background:

    • Investigating the structural properties of branched polymers like H-comb polymers is crucial for understanding their behavior in solution.
    • Continuum, tangent hard sphere models provide a simplified yet effective representation of polymer chains.

    Discussion:

    • The study utilizes a Monte Carlo pivot algorithm, a robust computational method for simulating polymer configurations.
    • Comparison between ideal and excluded volume regimes helps elucidate the impact of inter-chain interactions on polymer form factors.
    • The agreement between simulated and theoretical results validates the computational approach and the underlying polymer models.

    Key Insights:

    • Simulated form factors for ideal H-comb polymers with 241 and 931 beads show negligible variation, indicating size independence in this regime.

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    Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
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    Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

    Published on: September 26, 2016

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    MALDI-ToF MS Method for the Characterization of Synthetic Polymers with Varying Dispersity and End Groups
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    Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
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    Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
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    Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

    Published on: September 26, 2016

  • The observed form factors closely match theoretical predictions, confirming the accuracy of the model and simulation.
  • A minor divergence in form factor is noted between ideal and excluded volume conditions at larger distances, highlighting the influence of excluded volume effects.

    • Outlook:

    • Further simulations could explore a wider range of H-comb architectures and polymer lengths.
    • Investigating the impact of different solvent qualities and temperatures on H-comb polymer form factors would be beneficial.
    • Experimental validation of these simulation results would strengthen the understanding of H-comb polymer behavior.