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¹H NMR: Interpreting Distorted and Overlapping Signals

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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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When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...

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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...

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

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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.

2D NMR: Homonuclear Correlation Spectroscopy (COSY)

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Homonuclear correlation spectroscopy, or COSY, is a 2-dimensional NMR technique that provides information about coupled protons. Typically, the geminal and vicinal coupling are observed. For example, consider the COSY spectrum of ethyl acetate, where its 1D proton NMR spectrum is plotted along the vertical and horizontal axes with their corresponding chemical shift scale. Three spots on the diagonal corresponding to the three peaks in the 1D proton spectrum are called diagonal peaks. The COSY...

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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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Related Experiment Video

Updated: Mar 8, 2026

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

Published on: April 19, 2021

Peak picking multidimensional NMR spectra with the contour geometry based algorithm CYPICK.

Julia M Würz¹, Peter Güntert^2,3,4

¹Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt am Main, Max-von-Laue-Str. 9, 60438, Frankfurt am Main, Germany.

Journal of Biomolecular NMR

|February 5, 2017

Summary

CYPICK is a novel automated algorithm for identifying signals in multidimensional NMR spectra. It mimics manual analysis using geometric criteria, improving peak picking accuracy for protein structure determination.

Keywords:

Automated assignment CYANA Contour lines Peak list Peak picking Structure calculation

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15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

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Published on: April 19, 2021

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Area of Science:

Nuclear Magnetic Resonance (NMR) Spectroscopy
Structural Biology
Computational Chemistry

Background:

Automated signal identification in multidimensional NMR spectra is complex due to signal overlap, noise, and artifacts.
Existing methods lack universal acceptance and can be error-prone.

Purpose of the Study:

To develop a fully automated peak picking algorithm, CYPICK, that replicates manual spectroscopist analysis.
To evaluate CYPICK's performance against existing methods and its impact on subsequent automated processes.

Main Methods:

CYPICK analyzes NMR spectra by applying geometric criteria (extremality, circularity, convexity) to contour lines, replacing manual inspection.
Algorithm performance was assessed using diverse protein NMR spectra.
Comparison involved evaluating peak lists against manual and other automated methods.

Main Results:

CYPICK successfully identifies signals in multidimensional NMR spectra.
Peak lists generated by CYPICK favorably compare to those from other automated methods.
CYPICK-generated data improved the accuracy of automated chemical shift assignment and protein structure calculation.

Conclusions:

CYPICK offers a robust and automated solution for peak picking in NMR spectroscopy.
The algorithm enhances the reliability of downstream automated analyses like chemical shift assignment and structure determination.
CYPICK represents a significant advancement in processing complex NMR data for structural biology.