text: The disadvantages in "receptivity" are compensated by the high sensitivity of C NMR signals to the chemical environment of the nucleus, i.e. the chemical shift "dispersion" is great, covering nearly 250 ppm.  This dispersion reflects the fact that non-H nuclei are strongly influenced by excited states ("paramagnetic" contribution to shielding tensor. This paramagnetic contribution is unrelated to paramagnetism).  For example, most H NMR signals for most organic compounds are within 15 ppm. 
  The chemical shift reference standard for 
  C is the carbons in tetramethylsilane (TMS),
  whose chemical shift is set as 0.0 ppm at every temperature.