An NMR spectrum of an unknown compound obtained from a 400-MHz NMR spectrometer shows protons at a position 840 Hz downfield from the TMS.
(a) Determine the chemical shift of these protons.
(b) Determine their chemical shift in an 80-MHz NMR spectrometer.
(c) By how many Hz their chemical shift should be downfield from TMS using an 80-MHz NMR instrument?

• A. (a). Chemical shift = 2.1 ppm
  (b). Chemical shift = 2.1 ppm, the chemical shift of a given proton is the same regardless of the operating field and frequency of the spectrometer.
  168 Hz downfield from TMS
• B. (a). Chemical shift = 21 ppm
  (b). Chemical shift = 21 ppm, the chemical shift of a given proton is the same regardless of the operating field and frequency of the spectrometer.
  186 Hz downfield from TMS
• C. (a). Chemical shift = 2.1 ppm
  (b). Chemical shift = 4.2 ppm.
  680 Hz downfield from TMS
• D. (a). Chemical shift = 21 ppm
  (b). Chemical shift = 0.8 ppm.
  80 Hz downfield from TMS

Answer: (A)