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Related Concept Videos

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...
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
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.
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...

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Related Experiment Video

Updated: Jun 29, 2026

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
14:55

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy

Published on: September 17, 2017

Microsolvation and 13C-Li NMR coupling.

Rudolf Knorr1, Thomas Menke, Kathrin Ferchland

  • 1Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität, Butenandtstrasse 5-13, 81377 München, Germany. rhk@cup.uni-muenchen.de

Journal of the American Chemical Society
|October 3, 2008
PubMed
Summary
This summary is machine-generated.

A new empirical expression relates NMR coupling constants ((1)J(CLi)) in carbon-lithium compounds to the number of lithium nuclei and coordinated donor ligands. This finding may help determine unknown microsolvation numbers in organolithium aggregates.

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Area of Science:

  • Organometallic Chemistry
  • Nuclear Magnetic Resonance Spectroscopy

Background:

  • Nuclear Magnetic Resonance (NMR) spectroscopy is crucial for characterizing organolithium compounds.
  • Understanding the coordination environment around lithium nuclei is essential for predicting reactivity and structure.

Purpose of the Study:

  • To propose and validate an empirical expression correlating the (1)J(CLi) NMR coupling constant with structural parameters.
  • To investigate the influence of solvation and aggregation on (1)J(CLi) in various carbon-lithium (C-Li) compounds.

Main Methods:

  • Integration of NMR resonances for coordinated and free donor ligands (t-BuOMe, Et2O, THF).
  • Analysis of nuclear Overhauser correlations and determination of solid-state structures.
  • Application of the derived empirical expression to diverse C-Li compounds (monomeric, dimeric, tetrameric, and aggregates).

Main Results:

  • An empirical expression, (1)J(CLi) = L[n(a + d)](-1), was established, showing reciprocal dependence on lithium nuclei number (n) and ligand coordination sum (a + d).
  • Microsolvation numbers (d) correlate with observed changes in NMR chemical shifts for carbanionic (13)C(alpha), C(para), and p-H.
  • The expression demonstrates applicability across various C-Li compounds, including solvated and unsolvated aggregates.

Conclusions:

  • The (1)J(CLi) coupling constant can serve as a valuable tool for assessing unknown microsolvation numbers in organolithium species.
  • The study emphasizes the importance of analyzing (13)C NMR C-Li multiplet splitting for both fluxional and non-fluxional aggregates.