Topic 7 + 19: Analytical Techniques I, II Flashcards
What kind of information can you find through 13C NMR spectroscopy?
Number of carbon environments
Chemical shift
What is the reference molecule used in NMR
TMS (tetramethylsilane)
Why is TMS used as a reference molecule
- Inert so won’t react
- All H and C environments are identical so produces one sharp/ intense peak
- Peak at low chemical shift
- Easy to remove (low boiling point)
Why is a larger, more concentrated sample needed for 13C NMR rather than H NMR?
13C has a lower abundance than 1H
What information can you find through 1H NMR spectroscopy?
- Number of H environments
- Splitting patterns (n+1 rule)
- Area (ratio of Hs in each environment)
- Chemical shift
What does the presence of complex multiplets indicate?
Presence of a benzene ring
What could be happening if there is a complex/unexplained multiplet
2 overlapping signals from two environments which are very similar but slightly different
What is the stationary phase used in thin-layer chromatography (TLC)
Solid silica on a glass plate
What is the stationary phase used in column chromatography (CC)
Solid Silica
What is the stationary phase used in gas-liquid chromatography (GLC)
Microscopic liquid film on a solid support
What is the mobile phase used in thin layer chromatography (TLC)
Liquid solvent, e.g. water or organic
What is the mobile phase used in column chromatography?
Liquid solvent, e.g. water or organic
What is the mobile phase used in gas-liquid chromatography?
Inert carrier gas, e.g. nitrogen
What is the purpose of chromatography?
Separation of compounds in a mixture (analysis and identification)
What is the purpose of the mobile phase?
The more soluble (the stronger the interactions between the molecule and the mobile phase) a molecule is in the mobile phase AND the less soluble in the stationary phase (retention), the higher the retention factor is.
What is the purpose of the stationary phase?
To slow the molecules moving through the mobile phase - to retain them. Usually is a different type of interaction between the molecules in the stationary phase vs in the mobile phase.
Formula for Rf value
Rf = Retention factor
Rf = (distance travelled by substance)/(distance travelled by solvent front)
Explain high performance liquid chromatography (HPLC) and how it works.
- Essentially column chromatography
- Sample pumped through by solvent
- Stationary phase particles are smaller -> greater separation of compounds
- Detector at the end of the column
- Retention time = time taken from injection to detection
Explain what is gas chromatography and how does it work?
- Used for analysing gases, volatile liquids, solids in vapour form
- Stationary phase: long coiled column
- Mobile phase: inert carrier gas moves sample molecules through stationary phase
- In gas-liquid, a non-volatile liquid is the stationary phase
