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2. Chemical shifts - Number of resonance signals

The first piece of information required for the deduction of an NMR spectrum is the number of resonance signals that can be expected.

How can it be determined?

Recall what you have already learned:
  1. In the presence of a homogenous magnetic field, every 1H nucleus shows upon irradiation with an field of the proper frequency a resonance signal.
  2. The resonance signal of a 1H in a chemical compound is shifted compared to the signal of an isolated 1H, since the external magnetic field will be modulated by the secondary magnetic fields induced in the electrons in the neighborhood of the proton. Therefore 1H with identical electronic environments will show chemical shifts, i.e. signals at .
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Which of the following approaches will give you the right number of 1H signals in an NMR spectrum of a compound?

The number of signals in an NMR spectrum is equal to
  1. the total number of hydrogen atoms in the compound,
  2. the number of hydrogen containing groups in the molecule,
  3. the number of sterically equivalent groups of protons.