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Related Concept Videos

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.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not...
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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...
848
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

917
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.
917
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

946
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...
946
Atomic Nuclei: Nuclear Magnetic Moment00:59

Atomic Nuclei: Nuclear Magnetic Moment

1.0K
All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
1.0K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.2K
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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Exploring Nuclear Spin Conservation in the CH2 + H2 Reaction.

Yuki Miyamoto1,2, Masaaki Tsubouchi1,3, Takamasa Momose1

  • 1Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, BC V6T1Z1, Canada.

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Nuclear spin conservation is key in chemical reactions. This study reveals how nuclear spin rules apply to methylene and hydrogen reactions, offering insights into combustion and atmospheric chemistry.

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Area of Science:

  • Chemical Physics
  • Molecular Spectroscopy
  • Quantum Chemistry

Background:

  • Nuclear spin angular momentum is conserved in many molecular processes.
  • Its role in reactions with atomic rearrangements is not fully understood.
  • Methylene (CH2) and hydrogen (H2) reactions are fundamental in chemistry.

Purpose of the Study:

  • Investigate nuclear spin selection rules in CH2 + H2 reactions.
  • Clarify the reaction mechanisms of singlet and triplet methylene.
  • Determine the influence of nuclear spin on reaction pathways.

Main Methods:

  • High-resolution infrared spectroscopy.
  • Experiments conducted in quantum solid parahydrogen.
  • Analysis of nuclear spin distribution in reaction products.

Main Results:

  • Triplet methylene (3CH2) reactions follow predicted nuclear spin selection rules for stepwise mechanisms.
  • Singlet methylene (1CH2) reactions show deviations from direct insertion mechanism predictions.
  • Observed deviations in 1CH2 reactions attributed to energy excess or competing pathways.

Conclusions:

  • Nuclear spin conservation holds even for reactive intermediates like methylene.
  • Nuclear spin state detection is crucial for elucidating complex reaction mechanisms.
  • Findings impact understanding of hydrocarbon combustion and planetary atmospheric chemistry.