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Related Concept Videos

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

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The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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

Proton (¹H) NMR: Chemical Shift

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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...
1.9K
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
¹H NMR of Labile Protons: Deuterium (²H) Substitution00:48

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

963
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.
963
NMR Spectroscopy Of Amines01:19

NMR Spectroscopy Of Amines

9.3K
In proton NMR spectroscopy, primary amines and secondary amines showcase their N–H protons as a broad signal in the chemical shift range between δ 0.5 and 5 ppm. The exact position in this range depends on several factors, including sample concentration, hydrogen bonding, and the type of solvent used. Since amine protons undergo fast proton exchange in solution, the protons are labile and therefore do not participate in any splitting with adjacent protons. Thus, the observed peak is...
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Simulating Biomolecules with the Variable Protonation State: A Tutorial for Constant-pH Molecular Dynamics in NAMD.

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Constant-pH molecular dynamics simulations model systems with changing protonation states. This method allows for dynamic exploration of protonation shifts, yielding titration curves comparable to experimental data.

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Area of Science:

  • Computational chemistry
  • Biophysics
  • Biochemistry

Background:

  • Conventional molecular dynamics (MD) simulations often assume fixed protonation states.
  • Accurately modeling biological systems requires accounting for dynamic protonation state changes.

Purpose of the Study:

  • To provide a tutorial on applying constant-pH molecular dynamics simulations.
  • To highlight the advantages of constant-pH MD over conventional MD for specific systems.

Main Methods:

  • Utilizing constant-pH molecular dynamics simulations.
  • Actively exploring dynamic shifts in protonation states during simulation.
  • Analyzing simulation data to generate titration curves.

Main Results:

  • Constant-pH simulations successfully model systems with multiple protonation states.
  • The method allows for dynamic exploration of protonation shifts.
  • Generated titration curves can be compared with experimental results.

Conclusions:

  • Constant-pH molecular dynamics is a powerful technique for studying systems with variable protonation.
  • This approach offers a more realistic representation of protonation dynamics in simulations.
  • The method facilitates direct comparison between simulation and experimental titration data.