B correspondingly greater than Bo, the resonance value for the isolated proton (Eqs. (J1.13) and (J1.14)) Alternatively, if the applied field is held constant, the excitation frequency must be increased in order to bring about the resonance condition.The shielding constant ơ is an inconvenient measure of the chemical shift. Since absolute shifts are rarely needed and are difficult to determine, it is common practice to define the chemical shift in terms of the difference in resonance freequencies between that of the nucleus of interest (V.v) and a reference nucleus (Vref) by means of a dimensionless parameter s
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