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Related Concept Videos

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: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

990
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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Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

941
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: Two-Bond Coupling (Geminal Coupling)01:20

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1.0K
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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NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.4K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
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Valence Bond Theory02:42

Valence Bond Theory

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Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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Updated: Jul 13, 2025

Spin Saturation Transfer Difference NMR SSTD NMR: A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes
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Doubly Tuned Exchange-Correlation Functionals for Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory.

Konstantin Komarov1, Woojin Park2, Seunghoon Lee3

  • 1Center for Quantum Dynamics, Pohang University of Science and Technology, Pohang 37673, South Korea.

Journal of Chemical Theory and Computation
|October 16, 2023
PubMed
Summary
This summary is machine-generated.

New exchange-correlation (XC) functionals improve accuracy in time-dependent density functional theory (TDDFT) calculations. The developed DTCAM-VEE and DTCAM-AEE functionals offer enhanced performance for excitation energies and molecular dynamics simulations.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Theoretical Chemistry

Background:

  • Accurate prediction of molecular properties is crucial in computational chemistry.
  • Time-dependent density functional theory (TDDFT) is a widely used method for electronic structure calculations.
  • Developing improved exchange-correlation (XC) functionals is key to enhancing TDDFT accuracy.

Purpose of the Study:

  • To improve the accuracy of MRSF-TDDFT calculations by employing different XC functionals for reference and response parts.
  • To develop novel XC functionals based on the adaptive exact exchange (AEE) concept within the Coulomb-attenuating framework.
  • To evaluate the performance of the new functionals for vertical excitation energies, conical intersections, nonadiabatic molecular dynamics, charge-transfer states, and potential energy surfaces.

Main Methods:

  • Development of two new XC functionals: DTCAM-VEE and DTCAM-AEE.
  • Application of these functionals within the Multireference Second-Order Self-Consistent Field Time-Dependent Density Functional Theory (MRSF-TDDFT) framework.
  • Validation against experimental data and established theoretical benchmarks, including Thiel's set and BH&HLYP.
  • Assessment of performance for various molecular systems and properties, such as excitation energies, conical intersections, NAMD, charge-transfer states, and PESs.

Main Results:

  • DTCAM-VEE showed excellent agreement with Thiel's set for excitation energies (MAE: 0.218 eV, IQR: 0.327 eV).
  • DTCAM-AEE accurately reproduced conical intersections for trans-butadiene and thymine, and NAMD simulations on thymine.
  • DTCAM-AEE demonstrated exact 1/R asymptotic behavior for charge-transfer states and accurate PESs for the rPSB6 model.
  • DTCAM-AEE significantly improved upon BH&HLYP with MAE of 0.237 eV and IQR of 0.41 eV.

Conclusions:

  • Employing distinct XC functionals for reference and response calculations significantly enhances MRSF-TDDFT accuracy.
  • The newly developed DTCAM-VEE and DTCAM-AEE functionals provide a promising advancement in computational chemistry.
  • The methodology offers a new avenue for developing improved XC functionals applicable to various theoretical chemistry problems.