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Related Concept Videos

¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

1.3K
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...
1.3K
¹H NMR of Labile Protons: Deuterium (²H) Substitution00:48

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

944
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.
944
Proton (¹H) NMR: Chemical Shift01:07

Proton (¹H) NMR: Chemical Shift

1.8K
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...
1.8K
¹H NMR of Labile Protons: Temporal Resolution01:10

¹H NMR of Labile Protons: Temporal Resolution

1.2K
Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
1.2K
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

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

1.4K
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...
1.4K
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

897
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
897

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Related Experiment Video

Updated: Aug 9, 2025

Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy
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Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy

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Collective Proton Transfers in Cyclic Water-Ammonia Tetramers: A Path Integral Machine-Learning Study.

Emilio Méndez1, Pablo E Videla2, Daniel Laria1,3

  • 1Departamento de Química Inorgánica, Analítica y Química-Física and INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires Ciudad Universitaria, Pabellón II, 1428 Buenos Aires, Argentina.

The Journal of Physical Chemistry. A
|February 16, 2023
PubMed
Summary
This summary is machine-generated.

Machine learning simulations reveal proton transfer in water-ammonia cycles. Quantum effects reduce energy barriers and restore concertedness in these molecular isomerizations.

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Area of Science:

  • Physical Chemistry
  • Computational Chemistry
  • Chemical Physics

Background:

  • Isomerization processes in cyclic molecules are crucial for understanding chemical reactions.
  • Proton transfer dynamics in mixed water-ammonia systems are complex due to varying hydrogen bond strengths.

Purpose of the Study:

  • To investigate isomerization paths in mixed water-ammonia cyclic tetramers using advanced simulation techniques.
  • To elucidate the role of nuclear quantum effects on proton transfer and molecular chirality.

Main Methods:

  • Machine-learning-based path integral molecular dynamics simulations.
  • Analysis of free energy profiles and concertedness of proton transfers.
  • Inclusion of nuclear quantum effects to study tunneling regimes.

Main Results:

  • Mixed water-ammonia tetramers exhibit partial loss of concertedness in proton transfers, unlike monocomponent systems.
  • Polarized transition states and solvent-separated ion-pair configurations were observed in mixed tetramers.
  • Nuclear quantum effects significantly reduced activation free energies and introduced plateau-like features, indicating deep tunneling.

Conclusions:

  • The study highlights the impact of mixed components on proton transfer dynamics and molecular chirality.
  • Nuclear quantum effects play a vital role in modulating reaction pathways and energetics in these systems.
  • The findings provide insights into the fundamental mechanisms governing isomerization in cryogenic molecular clusters.