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:
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- In the presence of a homogenous magnetic field,
every 1H nucleus shows upon irradiation with an
field of the proper frequency a resonance signal.
- 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