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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: Three-Bond Coupling (Vicinal Coupling)01:22

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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 involved orbitals. The...
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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,...
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¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
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Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.9K
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...
1.9K
Van der Waals Interactions01:24

Van der Waals Interactions

73.2K
Atoms and molecules interact with each other through intermolecular forces. These electrostatic forces arise from attractive or repulsive interactions between particles with permanent, partial, or temporary charges. The intermolecular forces between neutral atoms and molecules are ion–dipole, dipole–dipole, and dispersion forces, collectively known as van der Waals forces.
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Spin-Component Scaling Methods for Weak and Stacking Interactions.

J Grant Hill1, James A Platts1

  • 1School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, U.K.

Journal of Chemical Theory and Computation
|December 3, 2015
PubMed
Summary
This summary is machine-generated.

New spin-component scaled for nucleobases (SCSN) parameters improve calculations of interaction energy for DNA base pairs. These SCSN parameters optimize density fitted local second-order Møller-Plesset perturbation theory (DF-LMP2) for accurate noncovalent interaction analysis.

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Area of Science:

  • Computational chemistry
  • Quantum chemistry
  • Biophysics

Background:

  • Accurate calculation of noncovalent interactions is crucial in molecular biology and drug design.
  • Second-order Møller-Plesset perturbation theory (MP2) is a common method, but can be computationally expensive.
  • Spin-component scaled variants offer a balance between accuracy and efficiency.

Purpose of the Study:

  • To develop and optimize new scaling parameters for spin-component scaled (SCS) density fitted local second-order Møller-Plesset perturbation theory (DF-LMP2).
  • To specifically tailor these parameters for evaluating interaction energies between nucleic acid base pairs.
  • To validate the applicability of the new parameters for a broader range of noncovalent interactions.

Main Methods:

  • Optimization of spin-component scaling parameters by minimizing root-mean-square (rms) interaction energy error.
  • Utilized a dataset of ten stacked nucleic acid base pairs for parameter training.
  • Tested the optimized parameters on a larger set of model complexes with varying noncovalent interaction types (dispersion, electrostatics).

Main Results:

  • Developed novel spin-component scaled for nucleobases (SCSN) parameters.
  • The optimal SCSN parameters set neglects antiparallel-spin electron pair contributions and scales parallel contributions by 1.76.
  • Achieved minimized rms interaction energy error for nucleic acid base pairs compared to literature values.
  • Demonstrated applicability to diverse noncovalent interactions beyond base pairs.

Conclusions:

  • The new SCSN parameters provide an accurate and efficient method for calculating interaction energies in nucleic acid base pairs.
  • These parameters enhance the utility of DF-LMP2 for studying biomolecular interactions.
  • The developed scaling approach shows promise for various noncovalent interaction studies in computational chemistry.