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Related Concept Videos

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

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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...
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Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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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,...
1.0K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.1K
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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Gibbs Free Energy and Thermodynamic Favorability02:23

Gibbs Free Energy and Thermodynamic Favorability

6.9K
The spontaneity of a process depends upon the temperature of the system. Phase transitions, for example, will proceed spontaneously in one direction or the other depending upon the temperature of the substance in question. Likewise, some chemical reactions can also exhibit temperature-dependent spontaneities. To illustrate this concept, the equation relating free energy change to the enthalpy and entropy changes for the process is considered:
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Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

1.1K
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...
1.1K
Thermodynamics: Activity Coefficient01:24

Thermodynamics: Activity Coefficient

1.7K
Activity is the measure of the effective concentration of the species in solution. It can be expressed as the product of the molar concentration of the species and its activity coefficient. The activity coefficient is a dimensionless quantity and depends on the total ionic strength of the solution.
The activity coefficient is a measure of the deviation from ideal behavior. When the ionic strength of the solution is minimal, the activity coefficient of an ionic species is close to unity, making...
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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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Host Spin-Crossover Thermodynamics Indicate Guest Fit.

Jieyu Zheng1, Larissa K S von Krbek2, Tanya K Ronson1

  • 1Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK.

Angewandte Chemie (International Ed. in English)
|October 20, 2022
PubMed
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Spin-crossover (SCO) cages offer potential for magnetic sensors. Guest molecules influence SCO cage spin states and cavity structure, enabling sensitive host-guest interaction studies.

Keywords:
Host-Guest ChemistryMetal-Organic CagesSpin Crossover

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Area of Science:

  • Supramolecular Chemistry
  • Materials Science
  • Coordination Chemistry

Background:

  • Spin-crossover (SCO) materials exhibit switchable spin states, enabling applications in sensing and molecular switches.
  • Metal-organic cages (MOCs) offer tunable cavities for host-guest chemistry and functional material design.

Purpose of the Study:

  • To investigate the influence of ligand design on SCO behavior in Fe(II) metal-organic cages.
  • To explore the interplay between guest encapsulation, SCO spin states, and cage cavity dynamics.
  • To utilize SCO thermodynamics for sensitive probing of host-guest interactions.

Main Methods:

  • Synthesis of imine-based ligands with varying heterocyclic aldehyde subcomponents.
  • Construction of homoleptic and heteroleptic Fe(II) SCO cages.
  • Variable-temperature magnetic susceptibility measurements to study SCO transitions.
  • Guest encapsulation studies and thermodynamic analysis of host-guest complexes.

Main Results:

  • Ligand donor strength tuning successfully modulated SCO behavior in Fe(II) cages.
  • The tetrahedral SCO cage demonstrated guest-dependent stabilization of spin states.
  • SCO cages exhibited differential guest affinities correlating with spin state-induced structural changes.
  • SCO thermodynamics provided sensitive insights into guest fit within the cage cavity.

Conclusions:

  • Fe(II) SCO cages can be rationally designed to exhibit diverse SCO properties.
  • Guest molecules play a critical role in modulating SCO cage spin states and structural dynamics.
  • SCO thermodynamics offers a complementary method to traditional binding studies for characterizing host-guest interactions.