✅19 - Modern Analytical Techniques II
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What is formed in a mass spectrometer?
A molecular ion
How is a molecular ion formed?
When a molecule looses an electron
What is the m/z value?
The mass/charge ratio
What is the m/z value the same as?
The molecular mass
What does high resolution mass spectrometry measure?
Precise masses
What can high resolution mass spectrometry be useful for identifying?
Compounds that appear to have the same Mr when rounded to the nearest whole number
What information does NMR give you?
About the structure of molecules
What does NMR stand for?
Nuclear Magnetic Resonance
How does NMR work?
A sample of a compound is put into a strong magnetic field and exposed to a range of different frequencies of radio waves Nuclei of certain atoms absorb energy from the radio waves
What information does Carbon-13 NMR give you?
About the number of carbon atoms that are in a molecule, and the environments that they are in
What information does High resolution Proton NMR give you?
About the number of hydrogen atoms that are in a molecule and the environments that they are in
What does the amount of energy that a nucleus absorbs depend on?
The environment that it is in
What is a nucleus shielded by?
Its surrounding electrons
What can electron shielding be affected by?
The other atoms and groups of atoms around the nucleus
How would an electronegative element affect the electron shielding?
It would reduce it, as the electrons would be drawn away
What does an atom’s environment depend on?
All the groups that it is connected to
What is used as a standard in NMR?
Tetramethylsilane - TMS
What are absorbances measured relative to?
TMS
Why is TMS used as a standard?
Because its absorption peak is at a lower frequency than all other molecules
What is chemical shift?
The difference in the radio frequency absorbed by the nuclei in the molecule being analysed and by the same nuclei as in TMS
What does the number of peaks on a C13 NMR spectrum show you?
The number of carbon environments
What do the chemical shifts show you?
The different carbon nuclei
What does proton NMR tell you?
The number of hydrogen environments
What splits the peaks in C13 NMR?
Spin-spin coupling