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Related Concept Videos

Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

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NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
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Spin–Spin Coupling: One-Bond Coupling01:17

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Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
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Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
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NMR Spectroscopy: Spin–Spin Coupling01:08

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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...
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Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

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All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
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Spin Saturation Transfer Difference NMR SSTD NMR: A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes
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Do Spin State and Spin Density Affect Hydrogen Atom Transfer Reactivity?

Caroline T Saouma1, James M Mayer1

  • 1Department of Chemistry, University of Washington, Campus Box 351700, Seattle, WA, USA.

Chemical Science
|January 14, 2014
PubMed
Summary
This summary is machine-generated.

This study challenges the idea that spin state is the main driver of hydrogen atom transfer (HAT) reactions. Instead, it suggests indirect effects and reaction diversity play larger roles.

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Area of Science:

  • Chemical kinetics
  • Reaction mechanisms
  • Organic chemistry

Background:

  • Hydrogen atom transfer (HAT) reactions are prevalent in chemical and biological systems.
  • Previous research suggested electronic spin state and spin-density are critical for HAT reactivity.

Purpose of the Study:

  • To present an alternative view on the role of spin state and spin-density in HAT reactions.
  • To analyze the fundamental kinetic factors influencing HAT reactivity.

Main Methods:

  • Fundamental kinetic analysis to evaluate the dominant effects in HAT reactions.
  • Examination of published computational studies on HAT reactions.

Main Results:

  • Kinetic analysis indicates that unpaired spin is not the dominant factor in HAT reactions.
  • Computational studies suggest spin state indirectly influences HAT, primarily through changes in driving force.

Conclusions:

  • The electronic spin state's role in HAT reactions is likely indirect, mediated by factors like driving force.
  • The diversity of HAT reactions and their overlap with proton-coupled electron transfer (PCET) may contribute to existing controversies.