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Related Concept Videos

¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
Proton (¹H) NMR: Chemical Shift01:07

Proton (¹H) NMR: Chemical Shift

Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
Absorption signals of all the protium nuclei in a...
¹H NMR of Labile Protons: Deuterium (²H) Substitution00:48

¹H NMR of Labile Protons: Deuterium (²H) Substitution

This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is the use of deuterium. Amongst the three isotopes of hydrogen, deuterium (2H) has a nucleus composed of one proton and one neutron. When the D2O solvent is added to a pure dry ethanol solution, its labile proton is substituted with deuterium.
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.
¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons01:03

¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons

Protons in identical electronic environments within a molecule are chemically equivalent and have the same chemical shift. The replacement test is a useful tool to identify chemical equivalence and predict NMR spectra. A substituent replaces each of the protons being examined and the resulting molecules are compared. If the same molecule is obtained, the protons are equivalent or homotopic. Replacement of any hydrogens in ethane by chlorine yields chloroethane because all six protons are...

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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

Published on: April 8, 2020

Electron proton-coupled transfers in [NH4][H3N]n (n = 1, 2) Rydberg clusters: A machine learning-path integral study.

Diego Hunt1,2, Daniel Laria1,3

  • 1Departamento de Física de la Materia Condensada, GIyA, CAC-CNEA, 1650 San Martín, Buenos Aires, Argentina.

The Journal of Chemical Physics
|July 9, 2026
PubMed
Summary
This summary is machine-generated.

This study explores ammonia Rydberg complexes using advanced simulations. Nuclear quantum effects significantly alter proton transfer and energetics, improving agreement with experimental data.

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Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
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Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex

Published on: July 27, 2022

Area of Science:

  • Physical Chemistry
  • Computational Chemistry
  • Quantum Mechanics

Background:

  • Rydberg complexes are crucial for understanding electron behavior in molecular systems.
  • Proton transfer dynamics in small clusters are complex and influenced by quantum effects.
  • Accurate theoretical models are needed to interpret experimental data for these systems.

Purpose of the Study:

  • Investigate structure, energetics, and proton transfer in [NH4][NH3]n (n=1, 2) Rydberg complexes.
  • Elucidate the role of nuclear quantum effects and thermal fluctuations.
  • Compare molecular-orbital Rydberg descriptions with solvated electron models.

Main Methods:

  • Path-integral molecular dynamics (PIMD) simulations.
  • Machine-learning techniques for enhanced sampling and analysis.
  • Quantum mechanical calculations of energetics and reaction pathways.

Main Results:

  • Unpaired negative charge localized outside the molecular framework, near NH4+ character.
  • Nuclear quantum effects increase computed vertical detachment energies, matching experiments.
  • Proton transfer pathways and free energy landscapes are significantly modified by quantum tunneling.

Conclusions:

  • Nuclear quantum effects are essential for accurately describing Rydberg complex energetics and dynamics.
  • PIMD and ML provide powerful tools for studying complex chemical systems.
  • Insights into charge localization and proton transfer mechanisms in ammonia clusters.