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Related Concept Videos

¹H NMR Signal Integration: Overview00:58

¹H NMR Signal Integration: Overview

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The intensity of a signal, which can be represented by the area under the peak, depends on the number of protons contributing to that signal. The area under each peak is shown as a vertical line called an integral, with the integral value listed under it, as seen in the proton NMR spectrum of benzyl acetate. Each integral value is divided by the smallest integral value to obtain the ratio of the number of protons producing each signal. The ratio reveals the relative number of protons and not...
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Two-Dimensional (2D) NMR: Overview01:12

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The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse....
1.7K
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

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

3.0K
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...
3.0K
¹H NMR: Complex Splitting01:13

¹H 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...
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NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

1.1K
When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
1.1K
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

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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...
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Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
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Projected Volume Method for Accurate Measurement of Cross-Peak Intensity in Two-Dimensional NMR Spectra.

Daisuke Kohda1, Seiichiro Hayashi2, Kyoko Furuita3

  • 1Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.

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|March 17, 2026
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A new projection technique (Proj-Vol) accurately measures trandolapril’s equilibrium constant, resolving previous inconsistencies in angiotensin-converting enzyme (ACE) inhibitor studies. This method ensures reliable data for understanding drug isomerization mechanisms.

Keywords:
13C1H1H homonuclear J‐couplingHSQC0NMRequilibrium constantpeak volumeprojectiontrandolapriltwo‐state exchange

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Area of Science:

  • Analytical Chemistry
  • Organic Chemistry
  • Biochemistry

Background:

  • Trandolapril, an angiotensin-converting enzyme (ACE) inhibitor, exhibits cis-trans isomerization in organic solvents.
  • Previous NMR studies reported inconsistent equilibrium constants due to variations in proton (1H) nuclei analysis.
  • Experimental resolution was needed to address discrepancies in trandolapril's isomerization equilibrium.

Purpose of the Study:

  • To develop and validate a novel method for accurate cross-peak volume measurement in 2D NMR spectra.
  • To determine a consistent equilibrium constant for trandolapril's cis-trans isomerization.
  • To resolve discrepancies in previous NMR studies of trandolapril.

Main Methods:

  • Development of the Proj-Vol method for measuring cross-peak volumes using 1D 13C projections.
  • Application of the Proj-Vol method to 2D 1H-13C HSQC spectra of trandolapril acquired with the time-zero HSQC (HSQC0) scheme.
  • Comparison of Proj-Vol method results with existing 2D cross-peak fitting methods.

Main Results:

  • The Proj-Vol method yielded consistent equilibrium constant values across multiple 1H nuclei.
  • Demonstrated that trandolapril possesses a single, consistent equilibrium constant.
  • The Proj-Vol method offers advantages including fewer fitting parameters, elimination of J-coupling considerations, and improved signal-to-noise ratio.

Conclusions:

  • The Proj-Vol method provides accurate cross-peak volume determination in 2D HSQC spectra.
  • Trandolapril exhibits a single equilibrium constant, consistent with its isomerization mechanism.
  • This new projection technique enhances the reliability of NMR studies for analyzing molecular exchange processes.