NMR Spectroscopy
NMR gives structural information about the molecule
NMR is an analysis technique used to work out the 3D structure of organic compounds
The way that NMR works is complicated but here is the basic:
1. Sample of compound placed in a strong magnetic field and exposed to a range of
different frequencies of low-energy radio waves.
2. The nuclei of certain atoms within the molecule absorbs energy from radio waves.
3. The amount of energy that a nucleus absorbs at each frequency will depend on the
environment it is in.
4. The pattern of absorption gives information about the position of certain atoms
within the molecule, and about how many atoms of that type the molecule contains.
5. Can place these bits of information together to work out the structure of the
molecule.
There are 2 types of spectroscopy need to know:
1. Carbon-13 NMR
- Gives information about the number of C atom in molecule.
- Environment C atoms in.
2. High resolution proton NMR
- gives information about number of H atoms in molecule.
- Environment H atom in.
Nuclei in different environments absorb different amounts of energy
A nucleus is partly shielded from the external magnetic field by it surrounding electrons.
Any other atom or group of atoms that are around a nucleus will also affect its amount
of electron shielding.
- E.g. if a C atom bonded to a more electronegative atom the amount of electron
shielding around the nucleus will decrease.
- This is because electrons are closer to electronegative atoms, which means that
the C atom is not shielded well.
This means that the nuclei in a molecule feels different magnetic fields depending on
their environments.
This means that the nuclei will absorb different amounts of energy at different
frequencies
It is theses difference in energy between environments that you are looking for in NMR
Spectroscopy.
An atoms environment depends on all the groups that it's connected to, going right
along the molecule, not just the atom it is bonded to
To be in the same environment, 2 atoms must be joined to the exactly same atom.
NMR gives structural information about the molecule
NMR is an analysis technique used to work out the 3D structure of organic compounds
The way that NMR works is complicated but here is the basic:
1. Sample of compound placed in a strong magnetic field and exposed to a range of
different frequencies of low-energy radio waves.
2. The nuclei of certain atoms within the molecule absorbs energy from radio waves.
3. The amount of energy that a nucleus absorbs at each frequency will depend on the
environment it is in.
4. The pattern of absorption gives information about the position of certain atoms
within the molecule, and about how many atoms of that type the molecule contains.
5. Can place these bits of information together to work out the structure of the
molecule.
There are 2 types of spectroscopy need to know:
1. Carbon-13 NMR
- Gives information about the number of C atom in molecule.
- Environment C atoms in.
2. High resolution proton NMR
- gives information about number of H atoms in molecule.
- Environment H atom in.
Nuclei in different environments absorb different amounts of energy
A nucleus is partly shielded from the external magnetic field by it surrounding electrons.
Any other atom or group of atoms that are around a nucleus will also affect its amount
of electron shielding.
- E.g. if a C atom bonded to a more electronegative atom the amount of electron
shielding around the nucleus will decrease.
- This is because electrons are closer to electronegative atoms, which means that
the C atom is not shielded well.
This means that the nuclei in a molecule feels different magnetic fields depending on
their environments.
This means that the nuclei will absorb different amounts of energy at different
frequencies
It is theses difference in energy between environments that you are looking for in NMR
Spectroscopy.
An atoms environment depends on all the groups that it's connected to, going right
along the molecule, not just the atom it is bonded to
To be in the same environment, 2 atoms must be joined to the exactly same atom.
