The basic principle of Nuclear Magnetic Resonance (NMR) is based on the behavior of certain atomic nuclei when placed in a strong magnetic field and exposed to radiofrequency (RF) radiation.
Here’s how it works step by step:
- Nuclear Spin:
Some atomic nuclei (such as ¹H, ¹³C, ¹⁹F, and ³¹P) possess a property called spin, which makes them act like tiny magnets. - Magnetic Field Alignment:
When these spinning nuclei are placed in a strong external magnetic field, they align themselves either:- With the magnetic field (lower energy state), or
- Against the magnetic field (higher energy state).
- Resonance Condition:
When a specific radiofrequency (RF) pulse is applied, nuclei in the lower energy state absorb energy and flip to the higher energy state. This process is called resonance. - Signal Detection:
When the RF field is turned off, the excited nuclei return to their original state, releasing the absorbed energy as a measurable signal. - Spectrum Formation:
These signals are recorded and transformed into an NMR spectrum, which provides information about the chemical environment of the nuclei in the molecule.
In short:
NMR spectroscopy works on the principle that nuclei with spin absorb radiofrequency radiation in a magnetic field at a frequency characteristic of their magnetic environment.
This absorption and emission of energy reveal valuable details about the structure, bonding, and environment of atoms within a molecule.