Spin-Spin Coupling (J)
Definition
Splitting of an NMR signal into a multiplet by adjacent magnetic nuclei. The n+1 rule predicts the number of lines for first-order systems, and the spacing in Hz is the coupling constant J that encodes geometry.
- Field
- NMR spectroscopy
- Effect
- Splitting of a signal into a multiplet by adjacent magnetic nuclei
- Prediction rule
- n+1 rule for first-order systems
- Unit of J
- Hertz (Hz)
- Encodes
- Molecular geometry
Common questions
Why is the coupling constant J reported in Hz rather than ppm?+
J is a fixed property of the bonding relationship between coupled nuclei and does not change with the instrument's magnetic field strength, unlike chemical shift, so it is reported in the field-independent unit of Hz.
How does spin-spin coupling help distinguish two structurally similar compounds in casework?+
The multiplet pattern and J values reveal how many neighbouring protons a given proton has and their spatial relationship, which can differentiate isomers or substitution patterns that a simple chemical shift comparison alone cannot resolve.
Related terms
- Chemical Shift (Delta)
- The position of an NMR signal on the frequency axis, expressed in parts per million (ppm) relative to a reference (TMS =...
- DEPT 135
- A 13C editing experiment that flips CH3 and CH peaks up, CH2 peaks down, and makes quaternary carbons disappear. Used to assign...
- Deuterated Solvent
- A solvent with most or all of its protons replaced by deuterium (CDCl3, DMSO-d6, D2O), used so the solvent itself is invisible...
- FID and Fourier Transform
- The free induction decay is the time-domain signal emitted by relaxing nuclei after the RF pulse. A Fourier transform converts the FID...
- Integration
- The third stage, in which laundered funds re-enter the legitimate economy as apparently clean wealth. Common integration mechanisms include real estate purchases,...