First 350 words of the document:
How many Hydrogen atoms in a molecule
How many different environments the Hydrogen atoms are in
Spin-Spin coupling helps you work out what Hydrogen atoms are next
to each other.
Nuclei with odd numbers of protons and neutrons have a spin, so have a
weak magnetic field.
Because Hydrogen nuclei are in effect just one proton, they also have a spin.
Under normal circumstances, protons in a molecule are all spinning in
different directions, so their spins cancel out.
However, if a strong magnetic field is applied, the protons will either align
in the same direction as the applied magnetic field or in the opposite
direction to the magnetic field. There tends to me more aligned protons,
because they are at a lower energy level than the protons whose spin is
against the external magnetic field. Therefore there is an overall
absorption of energy.
The amount of energy absorbed by protons depends on their environment
(where they are in the molecule). Different protons will feel different fields
depending on the electron shielding of the atoms around them, so will
absorb different amounts of energy at different frequencies.
Chemical shift relative to TMS (added for calibration purposes)
Each peak = a different environment
Area under the peak is proportional to the number of protons in that
Using a table, the environment of the protons causing each peak can be
worked out, and from this the structure of the molecule can be deduced.
Samples need to be dissolved in solvents, but the solvents must not contain
single protons to avoid interfering with the nmr spectrum. Deuterated
solvents (containing H2) are used.
Results in the splitting of peaks on the nmr spectrum
The magnetic fields of neighbouring protons interfere with each other
if the protons are on adjacent carbon atoms
Doublet = one neighbouring proton
Triplet = two neighbouring protons
Quartet = three neighbouring protons