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Related Concept Videos

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.
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...
Magnetostatic Boundary Conditions01:28

Magnetostatic Boundary Conditions

An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
Isothermal Processes01:21

Isothermal Processes

A thermodynamic process that occurs at constant temperature is called an isothermal process. Heat slowly flows into the system or out of the system to maintain thermal equilibrium. Processes involving phase changes like water evaporation into steam or freezing water into ice at a constant temperature are examples of Isothermal Processes.
An ideal gas can also undergo isothermal expansion or compression.
For example, consider 1 mole of an ideal gas inside an isolated cylinder at initial volume V...
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...
Magnetic Susceptibility and Permeability01:31

Magnetic Susceptibility and Permeability

In linear magnetic materials, like paramagnets and diamagnets, magnetization is proportional to the magnetic field intensity. The constant of proportionality, a dimensionless number, is called magnetic susceptibility. The value of the susceptibility depends on the type of material.
When diamagnetic materials are placed under an external magnetic field, the moments opposite to the field are induced. Hence, the susceptibility for diamagnets has a minimal negative value of 10-5–10-6. Since...

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Related Experiment Video

Updated: Jul 9, 2026

Sediment Core Extrusion Method at Millimeter Resolution Using a Calibrated, Threaded-rod
06:06

Sediment Core Extrusion Method at Millimeter Resolution Using a Calibrated, Threaded-rod

Published on: August 17, 2016

Coupled 142Nd-143Nd isotopic evidence for Hadean mantle dynamics.

Vickie C Bennett1, Alan D Brandon, Allen P Nutman

  • 1Research School of Earth Sciences, Australian National University, Canberra ACT, 0200 Australia. vickie.bennett@anu.edu.au

Science (New York, N.Y.)
|December 22, 2007
PubMed
Summary

Ancient Greenland rocks reveal early Earth

Area of Science:

  • Geochemistry and Isotope Geology
  • Early Earth History and Planetary Science

Background:

  • Understanding the initial chemical differentiation of Earth is crucial for deciphering planet formation.
  • Isotopic systems provide powerful tools for tracing early geological processes.
  • The neodymium (Nd) isotopic system, particularly 142Nd and 143Nd, offers insights into early mantle evolution.

Purpose of the Study:

  • To directly date the formation of chemically distinct silicate reservoirs in the early Earth.
  • To investigate the scale and persistence of early mantle heterogeneities.
  • To track the subsequent evolution and remixing of these early mantle domains.

Main Methods:

  • Analysis of coupled neodymium-142 (142Nd) and neodymium-143 (143Nd) excesses in 3.85-billion-year-old rocks from southwest Greenland.

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Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions
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Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

Published on: June 13, 2015

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Last Updated: Jul 9, 2026

Sediment Core Extrusion Method at Millimeter Resolution Using a Calibrated, Threaded-rod
06:06

Sediment Core Extrusion Method at Millimeter Resolution Using a Calibrated, Threaded-rod

Published on: August 17, 2016

Separation of Uranium and Thorium for 230Th-U Dating of Submarine Hydrothermal Sulfides
08:43

Separation of Uranium and Thorium for 230Th-U Dating of Submarine Hydrothermal Sulfides

Published on: May 20, 2019

Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions
11:50

Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

Published on: June 13, 2015

  • Comparison of 142Nd signatures in coeval ancient rocks from Greenland and Western Australia (>3.6 billion years old).
  • Utilizing the decay of extinct samarium-146 (146Sm) and long-lived samarium-147 (147Sm) to date early silicate reservoir formation.

    • Main Results:

    • Neodymium isotopic data directly date the formation of chemically distinct silicate reservoirs within the first 30-75 million years of Earth history.
    • Differences in 142Nd signatures between Greenland and Western Australian rocks reveal large-scale mantle heterogeneities present very early in Earth's history.
    • These heterogeneities persisted for at least the first billion years, with temporal 142Nd variations indicating incomplete remixing of early mantle domains.

    Conclusions:

    • Earth's mantle was chemically heterogeneous from its earliest stages, with distinct silicate reservoirs forming rapidly.
    • The isotopic signatures preserved in ancient rocks provide a direct record of these early differentiation processes.
    • The incomplete remixing of these early domains influenced the subsequent geochemical evolution of the mantle.