Isomerization (TLC) Procedures Flashcards
Components of proper labeling of TLC plate:
1) Mark ORIGIN as one TICK MARK 1cm up from the bottom of the plate
2) Lanes labeled to the right of the tick mark
Origin should NOT be …
A FULL LINE
–> Origin should be a TICK MARK
Spotting the TLC Plate Procedure:
1) Dip micropipette into sample
2) Try to visualize an imaginary point of intersection of origin and labeled lane to determine where to spot the sample
3) Lightly tap the micropipette at this point to dispense the sample
Why does the TLC sample need to be dissolved in a volatile solvent?
That way the solvent will EVAPORATE from the plate and therefore not interfere with the TLC run!
What was the purpose of methylene chloride in the isomerization experiment?
Served as the volatile solvent to allow for the application of the analyte to the TLC plate
What is methylene chloride AKA
Dichloromethane
Why can a spots on a TLC plate be visualized using UV light?
Because the plate has fluorescent components coating it
= Plate fluoresces
Wherever sample has been spotted, the fluorescent coating is covered up
= spots DO NOT fluoresce (appear dark)
TLC chamber set up:
1) Chromatography jar (flat-rim beaker = NO SPOUT)
2) Half-piece of filter paper pressed along side of jar
3) Solvent (mobile phase) in the jar
4) TLC plate on OPPOSITE wall of the filter paper
(should NOT be touching)
NOTE: Solvent level should be LOWER than the origin mark on the TLC plate!
5) Watch glass on top of jar to seal the system
What is the purpose of the piece of filter paper in the TLC setup?
It saturates the air inside the chamber with solvent vapors = prevents solvent (mobile phase) from evaporating from the plate during the development process!
= Even/consistent migration of the solvent and analyte up the plate! = better separation results
What happens if the solvent level in the developing chamber is at or above the origin of the TLC plate?
Samples will get submerged in the solvent and run off into the solvent rather than moving up the plate
–> Provides a new path for movement that the analyte will follow rather than going up the plate
What should be done once the solvent reaches ~0.5 cm from top of plate?
Remove the TLC plate and right away draw a line ACROSS the plate where the solvent has ended
= SOLVENT FRONT
Solvent Front
The furthest point a solvent travels in chromatography
After development, what should be done during UV visualization?
What should NOT be done?
The spots should be OUTLINED exactly as they appear (actual shape of the spots)
They should NOT simply be circled
After the isomerization reaction of dimethyl maleate, what is added to the mixture to crystallize out dimethyl fumarate?
Cold hexane
Why does hexane crystallize out dimethyl fumarate but not dimethyl maleate?
Because dimethyl maleate (CIS) has an MP LOWER than room temp!
= dimethyl maleate (CIS) is LIQUID at room temp! (= won’t form a solid precipitate!)
Whereas dimethyl fumarate is SOLID at room temp (Due to the better packing ability of the trans conformation!)
BUT, remember that BOTH are INSOLUBLE in hexane!!
