6.5.2: NMR Spectroscopy Flashcards
NMR
Nuclear magnetic resonance
NMR
use
used to determine the structure of a molecule
Two types of NMR
13C NMR
1H NMR
13C NMR
Gives information about how carbon atoms are arranged in a molecule
1H NMR
Gives information about how hydrogen atoms are arranged in a molecule
Nuclear environments
A nucleus is partially shielded from the effects of an external magnetic field by its surrounding electrons and any other groups of atoms that are around the nucleus.
What determines the overall effect of the external magnetic field on the nucleus?
The overall effect of the external magnetic field on each nucleus is different, depending on its environment within the molecule.
The size of the energy gap between a nucleus being aligned with or against an external magnetic field is determined by?
the strength of the magnetic field
Nuclei in different environments will absorb…
at different frequencies
What is NMR spectroscopy ‘looking for’
differences in absorption of energy between environments
What does an atoms environment depend on?
all the groups its connected to,
not just the atoms its actually bonded to
Chemical shift
Difference in the energy absorbed by nuclei in different environments relative to a standard substance.
Chemical shift is measured in
ppm
parts per million
Chemical shift standard
tetramethylsilane (TMS)
Why is TMS the standard
it has 12 hydrogens in identical environments and 4 carbons in indentical environments so it will produce a single absorption peak in both 13C and 1H NMR which is well away from the other peaks.
