Topic 19: Modern Analytical Techniques II
Topic 19A: Mass spectrometry
1. be able to use data from mass spectra to:
High resolution mass spectrometers
High resolution mass spectrometers can measure relative isotopic mass to 4dps. This means
relative atomic mass can be calculated to 4dps.
Suggest structures of simple organic compounds given Mrs to 4dp
Example: A high resolution mass spectrum shows a molecular ion peak at 98.0448. Which
compound is it?: C5H10N2, C6H10O, C7H14, C5H6O2
C5H6O2 = 5(12) + 6(1.0078) + 2(15.9990) = 98.0448
Calculate the accurate Mr of a compound, given RAM to 4dp, and therefore identify a compound
C4H10 and C3H6O both have Mrs fo 58 to the
nearest whole number. Using the RAMs of H, C,
N and O to 4dps:
C4H10 has an Mr of 58.1218
C3H6O has an Mr of 58.0789
This means they can be distinguished.
Topic 19B: Nuclear Magnetic Resonance (NMR)
2. understand that 13C NMR spectroscopy provides information about the
positions of 13C atoms in a molecule
Nuclear magnetic resonance (NMR)
NMR helps worm out the structure of organic molecules.
How it works:
1. Sample is placed in strong magnetic field and exposed to different frequencies of radio
waves
2. The nuclei of certain atoms within the molecule absorb energy from the radio waves
3. The amount of energy each nucleus absorbs depends on the environment it’s in
4. The absorption patterns tell you about the positions of the atoms in the molecule and
how many there are
Carbon NMR
13
C NMR tells you about the number of carbons in a molecule and the environment they are in.
The electrons surrounding a nucleus shield it from the magnetic effects. Any other atoms or
groups of atoms bonded to that atom will also affect the shielding e.g. O bonded to C decreases
the shielding on C as electrons are pulled away from C.
Topic 19A: Mass spectrometry
1. be able to use data from mass spectra to:
High resolution mass spectrometers
High resolution mass spectrometers can measure relative isotopic mass to 4dps. This means
relative atomic mass can be calculated to 4dps.
Suggest structures of simple organic compounds given Mrs to 4dp
Example: A high resolution mass spectrum shows a molecular ion peak at 98.0448. Which
compound is it?: C5H10N2, C6H10O, C7H14, C5H6O2
C5H6O2 = 5(12) + 6(1.0078) + 2(15.9990) = 98.0448
Calculate the accurate Mr of a compound, given RAM to 4dp, and therefore identify a compound
C4H10 and C3H6O both have Mrs fo 58 to the
nearest whole number. Using the RAMs of H, C,
N and O to 4dps:
C4H10 has an Mr of 58.1218
C3H6O has an Mr of 58.0789
This means they can be distinguished.
Topic 19B: Nuclear Magnetic Resonance (NMR)
2. understand that 13C NMR spectroscopy provides information about the
positions of 13C atoms in a molecule
Nuclear magnetic resonance (NMR)
NMR helps worm out the structure of organic molecules.
How it works:
1. Sample is placed in strong magnetic field and exposed to different frequencies of radio
waves
2. The nuclei of certain atoms within the molecule absorb energy from the radio waves
3. The amount of energy each nucleus absorbs depends on the environment it’s in
4. The absorption patterns tell you about the positions of the atoms in the molecule and
how many there are
Carbon NMR
13
C NMR tells you about the number of carbons in a molecule and the environment they are in.
The electrons surrounding a nucleus shield it from the magnetic effects. Any other atoms or
groups of atoms bonded to that atom will also affect the shielding e.g. O bonded to C decreases
the shielding on C as electrons are pulled away from C.
