Where H C and H R are the resonance frequencies of the applied magnetic field for compounds C and R, respectively, and ϭ C and ϭ R are the resulting shielding tensors. Ramsey devised an expression for calculating the NMR shielding tensor ϭ, as such for most solution NMR applications the shielding tensor ϭ can be replaced by a scalar quantity σ to give the following equation: