The gyromagnetic ratio, often denoted by the symbol γ (gamma), is a fundamental physical constant that characterizes the interaction between the magnetic moment of a nucleus and an external magnetic field. In the context of NMR spectroscopy, the gyromagnetic ratio determines the resonant frequency at which a particular nucleus will absorb electromagnetic radiation in the presence of a magnetic field.
For a given nucleus, the gyromagnetic ratio is a measure of how
rapidly the nucleus precesses (rotates) around the direction of an applied
magnetic field when subjected to a radiofrequency pulse. It is expressed in
units of radian per second per unit magnetic field strength (usually in units of
MHz/Tesla). In NMR, the gyromagnetic ratio is a key factor in determining the
resonance frequency of a nucleus in a magnetic field.
For carbon-13 (13C) nuclei, the gyromagnetic ratio is
approximately 10.7056 MHz/Tesla. This value is smaller than the gyromagnetic
ratio of hydrogen-1 (1H) nuclei, which is approximately 42.5775 MHz/Tesla. The
smaller gyromagnetic ratio of 13C nuclei contributes to the lower frequency of
the resonance observed in 13C NMR spectroscopy compared to 1H NMR spectroscopy.
In summary, the gyromagnetic ratio is a property specific to
each type of nucleus and plays a critical role in determining the NMR resonance
frequency and behavior of that nucleus in a magnetic field.