NMR and analysis Flashcards
outline the process of thin layer chromatography
- draw pencil line on plate and put spot of mixture on line
- dip bottom of plate into solvent
- solvent will move up and substances in mixture will separate out
- take out when solvent near top and mark the line
Rf value =
distance by spot / distance by solvent
what causes substances to separate out in TLC ?
- diff substances attract to the surface of the plate differently (adsorption)
- strong adsorption means will move slower so travel less
state the mobile phase in TLC
the solvent
state the stationary phase in TLC
the mixture (fluoresces UV light)
what is the retention time for gas chromatography ?
time for substances to pass through coiled tube to reach detector
In a gas chromatography graph, how is retention time found ?
time from zero to the peak
In a gas chromatography graph, how is relative amount of each substance found ?
area under peak
how does solubility affect retention time ?
more soluble will spend more time dissolved so will take longer to reach detector
how does boiling point affect retention time ?
high boiling point will spend more time condensed as a liquid than a gas, so take longer to reach detector
how does temperature affect retention time ?
high temp will shorten time for all substances as substance will be evaporated as a gas for longer
what is used as the standard for carbon-13 NMR ?
TMR (tetramethylsilane)
what is the name for the effect of H-NMR splitting ?
spin-spin coupling
what must be done with the solvent for H-NMR ?
- hydrogen nuclei from solvent (water/ethanol…) must be replaced with deuterium (D) so that solvent doesn’t effect peaks
- known as deuterated solvent
how can OH and NH be identified in H-NMR ?
- run two spectra of molecule, one w/ deuterium oxide (D2O)
- deuterium will swap w/ OH / NH, causing the peak to disappear
