Physical chemistry

Nuclear magnetic resonance (NMR)

NMR uses nuclear spin in a magnetic field to infer chemical environments, spin interactions and molecular structure.

A nucleus with spin and magnetic moment splits into levels in B₀. The Larmor frequency scales with γB₀; electron shielding shifts resonance with chemical environment.

Spin and chemical environment

NMR uses nuclear spin in a magnetic field to infer chemical environments, spin interactions and molecular structure.

Definition: Core definition

Chemical shift δ is the relative frequency offset from a reference, usually in ppm so it is largely independent of field strength.

\omega_0=\gamma B_0,\qquad \delta=10^6\frac{\nu-\nu_{ref}}{\nu_{ref}}\;\mathrm{ppm}

Example: Worked example

Apply the model to a simple case: In proton NMR of ethanol, CH₃, CH₂ and OH environments commonly give distinct signals; spin-spin coupling can split them into multiplets.

Solution

In proton NMR of ethanol, CH₃, CH₂ and OH environments commonly give distinct signals; spin-spin coupling can split them into multiplets.

Chemical shift δ is the relative frequency offset from a reference, usually in ppm so it is largely independent of field strength.

Spin and chemical environment
Quantity	Model / rule
Key relation	NMR uses nuclear spin in a magnetic field to infer chemical environments, spin interactions and molecular structure.
Meaning / use	In proton NMR of ethanol, CH₃, CH₂ and OH environments commonly give distinct signals; spin-spin coupling can split them into multiplets.

What expression is the nuclear-spin Larmor frequency proportional to?

Which statement best matches the model described?

References

Malcolm H. Levitt (2008). Spin Dynamics