NMR Flashcards
what is resonance with a field?
a photon with specific energy can cause a spin flip
what are the the spins of nucleons?
nucleons can either be parallel or antiparallel
what is Belec?
tiny magnetic field
what is B0?
external magnetic field
what do the electrons in do?
electrons generate a B elec which opposes B0, making the nucleus have a weaker magnetic field
electrons shield the nucleus from B0
relationship between electrons and shielding?
greater electron density the greater the shielding effect
how do electronegative elements gain electron density?
‘electronegative elements attract electron density from other adjacent groups’
therefore more electrons means the atom feels less effect from the B0 so B eff is lower therefore the delta E is lower and lower energy photon is absorbed
why are different energy photons absorbed by each atom?
because magnetic field each atom feels is different because of how shielded they are therefore the difference in energy (delta E) is different
what is B eff?
the magnetic field each atom feels
what is 1ppm equal to in Hz?
300Hz
what is multiplicity?
signal shape
how do you present a 3 coupling constant?
3J which are typically 7Hz
so 3 bonds away
what are OH protons described as?
unexchangeable
broader peaks
unlikely to split other protons
what happens when D2O is added?
OH will be exchanged with deuterium which doesn’t appear on the proton spectrum
how is NMR sample prepared?
‘2 – 20 mg of solid dissolved in ~ 1 mL of deuterated solvent
Filter through cotton wool into NMR tube to ~ 4 cm depth
Place NMR tube into spinner using depth gauge.’
