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Related Concept Videos

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

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.
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Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...
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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 in...
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Nuclear quadrupole coupling constants for N2O: experiment and theory.

Alex Brown1, Roderick E Wasylishen

  • 1Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2. alex.brown@ualberta.ca

The Journal of Physical Chemistry. A
|September 8, 2012
PubMed
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Accurate nuclear quadrupole coupling constants (NQCCs) for N(2)O require advanced computational methods like CCSD(T) and MRCI. These methods accurately predict NQCCs and explain electric field gradient modifications in van der Waals complexes.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

  • Nuclear quadrupole coupling constants (NQCCs) are crucial for understanding molecular electronic structure.
  • Previous studies have explored NQCCs in N(2)O, but accurate prediction remains challenging.
  • Experimental NMR data provides valuable benchmarks for theoretical calculations.

Purpose of the Study:

  • To determine accurate NQCCs for nitrogen and oxygen nuclei in N(2)O using various computational methods.
  • To evaluate the performance of different theoretical approaches in predicting NQCCs.
  • To investigate the influence of intermolecular interactions on electric field gradients (EFGs).

Main Methods:

  • Ab initio quantum chemical calculations employing MP2, QCISD, DFT (B3LYP, PBE0, B3PW91), CCSD, CCSD(T), CASSCF, and MRCI.
  • Utilized correlation-consistent basis sets for high accuracy.
  • Analysis of (14)N and (17)O NMR relaxation data in gas phase and various solvents.
  • Ab initio computations on the FH···N(2)O complex to model van der Waals interactions.

Main Results:

  • CCSD(T) and MRCI methods accurately predict NQCCs for central and terminal nitrogen atoms in N(2)O.
  • Spin-rotation and magnetic shielding tensors were computed and compared with experimental data.
  • (14)N NMR relaxation data indicates modifications of EFGs at nitrogen nuclei in solvent complexes.
  • Ab initio calculations confirm significant EFG changes induced by a single perturber (FH).

Conclusions:

  • Advanced coupled-cluster and multi-reference configuration interaction methods are essential for accurate NQCC prediction in N(2)O.
  • Intermolecular interactions, such as those in van der Waals complexes, significantly alter EFGs at the nitrogen nuclei.
  • The study provides a reliable theoretical framework for understanding NQCCs and EFG dynamics in N(2)O.