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Describe the factors affecting the coupling constant in NMR.
Accepted Answer
The coupling constant (J) in NMR is influenced by several factors:
Distance: J values decrease with increasing distance between coupled nuclei. The closer the nuclei are, the stronger the coupling interaction.
Dihedral angle: The dihedral angle between the coupled nuclei influences coupling strength. A trans (180°) arrangement often leads to larger coupling constants than a gauche (60°) arrangement.
Electronegativity of substituents: Electron-withdrawing groups near the coupled nuclei can increase J values.
Hybridization: The hybridization state of the coupled atoms affects coupling strength, with sp3 carbons showing weaker coupling than sp2 carbons.
Presence of multiple bonds: J values for nuclei connected by multiple bonds are often larger than those for single bonds.
Magnetic field strength: J values are independent of the applied magnetic field strength.
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