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Related Concept Videos

Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
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...
2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)01:19

2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)

Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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 slanted or...
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.
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.

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Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy
09:57

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Published on: July 25, 2022

Doubly compensated multiplicity-edited HSQC experiments utilizing broadband inversion pulses.

Haitao Hu1, Krish Krishnamurthy

  • 1Discovery Chemistry Research and Technologies, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN 46285, USA. hu haitao@lilly.com

Magnetic Resonance in Chemistry : MRC
|April 3, 2008
PubMed
Summary

We developed new nuclear magnetic resonance (NMR) pulse sequences using broadband inversion pulses (BIPs) that improve proton-180-degree pulse performance. These enhanced sequences offer greater sensitivity and tolerance to magnetic field variations in NMR spectroscopy.

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Generation and Coherent Control of Pulsed Quantum Frequency Combs
06:42

Generation and Coherent Control of Pulsed Quantum Frequency Combs

Published on: June 8, 2018

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Last Updated: Jul 6, 2026

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy
09:57

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy

Published on: July 25, 2022

Generation and Coherent Control of Pulsed Quantum Frequency Combs
06:42

Generation and Coherent Control of Pulsed Quantum Frequency Combs

Published on: June 8, 2018

Area of Science:

  • Nuclear Magnetic Resonance (NMR) Spectroscopy
  • Biophysical Chemistry
  • Organic Chemistry

Background:

  • Heteronuclear Single Quantum Coherence (HSQC) experiments are crucial for structural elucidation in NMR.
  • Existing CRISIS-HSQC and PEP-HSQC methods utilize conventional pulses, which can be limited by B(1) field inhomogeneity and pulse length.

Purpose of the Study:

  • To introduce novel, doubly compensated multiplicity-edited HSQC pulse sequences.
  • To enhance NMR sensitivity and robustness by replacing conventional pulses with broadband inversion pulses (BIPs).

Main Methods:

  • Development of new HSQC pulse sequences incorporating computer-optimized broadband inversion pulses (BIPs).
  • Replacement of conventional rectangular 180-degree proton pulses with BIPs.
  • Replacement of adiabatic carbon 180-degree pulses with shorter BIPs, while retaining adiabatic sweeps for J-independent coupling constant refocusing.

Main Results:

  • The proposed sequences demonstrate superior inversion performance and tolerance to B(1) field inhomogeneity compared to conventional methods.
  • A significant sensitivity gain was observed, primarily attributed to the improved B(1) field inhomogeneity tolerance of BIPs.
  • The modified sequences maintain the J-independent refocusing advantage of CRISIS-HSQC.

Conclusions:

  • The novel HSQC pulse sequences offer enhanced sensitivity and robustness for NMR spectroscopy.
  • The use of BIPs represents a significant improvement over conventional pulse methods in HSQC experiments.
  • These sequences are readily adaptable for (19)F--(13)C correlation spectroscopy.