6.3.2 spectroscopy Flashcards
what does NMR stand for
nuclear magnetic resonance
how does NMR work
sample is placed in a strong magnetic field and exposed to different frequencies of radio waves
nuclei of some atoms absorb energy from radio waves, amount of energy depends on the environment it is in
the pattern of absorption can tell us positions and amount of atoms
what is carbon-13 NMR
it gives you information about the number of carbon atoms in a molecule and the environments they are in
what is high resolution proton NMR
gives information about the number of hydrogen atoms and the environments they are in.
how does shielding effect absorption
groups around the atom effect its electron shielding so it absorbs different frequencies based on its environment
what is TMS (tetramethylsilane)
it is used as a reference as it has absorption lower than most molecules and produces a peak in both NMR types. this is put at 0
what is the chemical shift
the difference in radio frequency absorbed by the nuclei in the molecule being analysed and that absorbed n the same nuclei in TMS
what is chemical shift measured in
parts per million
steps of analysing carbon-13 NMR
- number of peaks is the number of carbon environments.
- look at chemical shifts on the diagram to determine environments
- try possible structures
steps of analysing proton NMR
- each peak represents a hydrogen environment
- relative area under the peak tells us the relative numbers of hydrogen atoms in the environment. or we look at the ratio of peaks to find it.
- splitting pattern tells us how many H atoms in adjacent environments. Take 1 away from the number of peaks
figure out the structure
why do we use deuterated solvents
there is no hydrogen atoms so they don’t produce a peak on the spectrum
how an we identify OH and NH groups in proton NMR as the chemical shift is variable
run another NMR adding a bit of deuterium oxide D2O. the peaks disappear because they swap with deuterium.
