Chapter 29 - Chromatography And Spectroscopy Flashcards
What makes up a TLC plate
Plastic/ glass sheet sprayed with solid silica
Adsorption
How the solid silica holds substances to its surface in TLC
Uses of TLC
Drug analysis and forensic science
Rf value formula
Distance by solute/ distance by solvent
How to view invisible solvents of TLC
Spray with developing agent
TLC: retention
Interaction between solute and stationary phase
Polar solute and polar stationary phase = strong adsorption more retention so lower rf
TLC: solubility
Between solute and mobile phase
Polar solvent non polar solute spends more time adsorbed to stationary phase so lower rf
Gas chromatography stationary phase
High boiling liquid adsorbed to solid support
Gas chromatography mobile phase
Inert carrier gas (helium)
Retention time
How long substance stays in gas chromatography thing
Polar stationary phase, non polar solute has lower retention time
Test for alkenes
Mix with bromine water, alkene, cause rapid decolourisation of bromine water
Colour change: orange to colourless
Test for Haloalkanes
Add aqueous silver nitrate - forms a precipitate
Chloro: white
Bromo: cream
Iodo: yellow
Test for primary secondary alcohol and aldehyde
Add acidified potassium dichromate (VI) and heat
Colour change from Orange to Green
Test for carboxylic acid
Add a carbonate such as sodium carbonate effervescence occurs
Carbon 13 NMR number of carbon environments
The number of peaks
Carbon 13 NMR type of carbon environment
The chemical shift
Proton number of proton environment
Number of peaks
Proton, NMR number of protons in each environment
Integration trace/ratio of relative peak areas
Proton NMR n +1 rule
n = no. H+ on adjacent carbons
+1 for (H+)s of environment
What is TMS
Reference compound
Has 12 protons in the same environment, so the most shielded they can possibly be
Assigned a chemical shift of 0 ppm
Advantages of TMS as a reference compound
Chemically inert
Soluble in most organic solvents
Proton, NMR, shielding
Electron shield protons from external magnetic fields decrease in chemical shift
Proton, NMR deshielding
Electronegative groups, attract electrons away from the protons decreasing shielding equals increased chemical shift
Problem with OH and NH on proton NMR
The protons aren’t bonded to a carbon: hard to identify as they have a broad/ variable chemical shift
Proton exchange for hydroxyl and Amine groups
Run anymore as normal
Add dueterated solvent
Run NMR again
Any peaks that disappear, the second time are OH/NH groups
How old is proton exchange with deuterium work
It’s exchanges and replaces labile protons of OH/NH
Why don’t deuterated solvents show on proton NMR spectra
D is and isotope of H and doesn’t create a chemical shift
