Larmor equation

(Joseph Larmor, 1857-1942, British physicist), equation stating that the resonant frequency n (angular frequency w) observed in an NMR experiment is proportional to the overall (macroscopic and microscopic) magnetic field B:

2pn = w = df/dt = gB

where g is the gyromagnetic ratio. A system of nuclear spins will therefore exhibit shifts in the Larmor frequency dependent on the microscopic magnetic surroundings, i.e. the local B field, giving rise to the so-called chemical shift. The Larmor resonant frequencies for H-1 and P-31 are given below:

GvS