NMR Flashcards
What is NMR?
An analytical technique used for determining what the structure of molecules and compounds are
How does NMR work?
Uses samples containing carbon 13 isotopes or hydrogen atoms
Since their odd atomic mass gives the atoms a nuclear spin which produces peaks on an NMR spectra
The difference in the energy of the spin states varies and is affected by the environment the atoms are in
Therefore we can gain structural informal about the types of groups present
What is the reference molecule used for NMR?
TMS (tetramethylsilane)
Why is TMS used as a reference molecule?
All the hydrogen’s and carbons are in equivalent environments so there is only one peak produced
Non toxic
Inert and will not affect the sample
Low boiling point and is volatile so can easily be removed
What do the peaks on a carbon 13 spectra mean?
The number of peaks on C13 is equivalent to the number of different environments the carbon atoms are in
What is the integration trace in proton NMR?
The number of hydrogen atoms that are producing that peak
Why does high resolution proton NMR provide more information about the environments present?
It can show us splitting patterns in the hydrogen atom peaks
The peaks are split into N+1 peaks where N is the number of direct neighbours.
1 neighbour- 2 peaks
2 neighbours - 3 peaks
3 neighbours - 4 peaks
What must be done to the sample before NMR Is carried out?
The compounds in the sample must be dissolved
Usually organic compounds so dissolved in organic solvents
Why must specific solvents be used in NMR?
Solvents must not contain hydrogen as they would then produce a peak on the spectra
What are the common solvents used for NMR?
CDCl3
Uses deuterium (heavy hydrogen as the mass number is 2 so will not produce a peak)
Deuterium oxide (heavy water)
Tetrachloromethane
