20 Organic synthesis, NMR & Chromatography Flashcards
Standard Molecule for NMR
TMS Tetramethyl silane
What solvents are used in NMR
CCl4 or deuterated solvents like CDCl3 or D2O
Deuterated as even numbers of protons are required to prevent interacting with the magnetic field.
Why is the standard molecule used?
TMS is:
Has 4 identical C/H environments
inert
non-toxic
Voltaile (easily separated from mixture)
What does the number of peaks mean in NMR?
Different C/H environments
What does O do to chemical shift?
Electronegativity causes a shift left.
For symmetrical molecules, what does NMR look like?
Integral/ratio of molecules must be considered to deduce the molecule along with formula given.
Same C/H environments due to symmetry heightens the same peak.
For H NMR, what is spin-spin coupling?
n+1 rule where n is H on adjacent C and the 1 is the original H.
Singlet to quartet.
How does chromatography work?
More soluble samples= higher Rf value, moves further = higher affinity to Mobile Phase.
Less soluble samples = lower Rf value, moves shorter= higher affinity to Stationary Phase.
GC-MS?
Gas chromatography then mass spec.
Used to identify compounds
Faster and more accurate.
Formula for Rf value?
Distance by sample/solvent front.
What is TLC?
Metal plate
Thin layer silica
Dried in fume cupboard to reduce toxic fumes.
UV lamp/Developing agent such as Iodine or Ninhydrin.
Column Chromatography?
Vertical column packed with solid, powdered substance.
Solvent with sample added.
Differing affinities= different retention times (Rf).
Retention time= time taken to drip out of tap at base of column.
Gas chromatography?
Thin tube packed with solid,powdered substance.
High pressure gas as mobile phase.
Sample injector with voltaile sample.
Retention time measured.
