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Related Concept Videos

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

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

1.2K
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...
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¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.3K
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...
1.3K
2D NMR: Overview of Heteronuclear Correlation Techniques01:18

2D NMR: Overview of Heteronuclear Correlation Techniques

612
Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an X-nucleus, such as carbon-13 or nitrogen-15. This method is commonly used in nuclear magnetic resonance (NMR) spectroscopy to gain insights into complex chemical compounds' structural and compositional aspects. A typical heteronuclear correlation spectrum displays X-nucleus chemical shifts on one axis and a proton spectrum on the other...
612
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

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

1.5K
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.
1.5K
Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

4.4K
For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
4.4K
2D NMR: Overview of Homonuclear Correlation Techniques01:16

2D NMR: Overview of Homonuclear Correlation Techniques

515
Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...
515

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Related Experiment Video

Updated: Dec 13, 2025

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

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Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra.

Todd M Alam1, Joshua P Allers1, Brad H Jones1

  • 1Department of Organic Materials Science, Sandia National Laboratories, Albuquerque, NM 87185, USA.

International Journal of Molecular Sciences
|July 26, 2020
PubMed
Summary
This summary is machine-generated.

Static solid-state 1H NMR spectroscopy reveals dynamic heterogeneities in thermoset polymers. This method quantifies activation energies, aiding in understanding polymer curing and dynamics near the glass transition temperature (Tg).

Keywords:
NMRchain dynamicspolymerssecond moment

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Area of Science:

  • Polymer Science
  • Materials Science
  • Spectroscopy

Background:

  • Thermoset polymers can achieve full cure below their glass transition temperature (Tg) due to dynamic and chemical heterogeneities.
  • Nuclear Magnetic Resonance (NMR) spectroscopy is crucial for understanding molecular dynamics in polymers.

Purpose of the Study:

  • To utilize static solid-state 1H NMR spectroscopy to measure chain dynamics activation as a function of temperature.
  • To explore the impact of activation energy and correlation time distributions on 1H NMR M2 analyses.
  • To demonstrate the measurement of dynamic activation energy distributions from M2 temperature behavior.

Main Methods:

  • Static solid-state 1H NMR spectroscopy was employed.
  • The NMR line shape second moment (M2) was analyzed as a function of temperature.
  • Normalized reference curves were used to analyze M2 temperature variations.
  • Dynamic heterogeneity in thermosetting polymers was systematically varied.

Main Results:

  • Increasing polymer segmental chain fluctuations near Tg cause dynamic averaging of proton-proton dipolar couplings, reducing M2.
  • Distributions in dynamic correlation times are common in polymer systems.
  • The study demonstrates that distributions in dynamic activation energies can be quantified from M2 temperature dependence.
  • An example analysis for thermosetting polymers with varied dynamic heterogeneity is presented.

Conclusions:

  • Static solid-state 1H NMR spectroscopy is effective for probing chain dynamics and activation energies in polymers.
  • The M2 temperature behavior provides insights into dynamic heterogeneity and activation energy distributions.
  • This approach offers a method to understand curing processes and material properties in thermosets.