Orgo lab techniques Flashcards
What is extraction?
Using a solvent to separate solution. You choose a solvent that the desired solution is soluble in.
If you want to extract a basic solution from a mixture, what solvent do you use?
a dilute acidic solvent which protonates the base, making it positive and increasing its solubility.
you use dilute base to extract an acid.
what is the aqueous layer and organic layer in an extraction?
the aqueous layer includes the solvent and the extracted compound solution.
organic is whatever is left
what is thin-layer chromatography (TLC)?
This separates based on polarity. It is preferentially used for smaller compounds
A non-polar solvent is used in the mobile phase, therefore non-polar compounds travel much further then polar compounds.
what is a TLC Rf factor? (%)
the distance the compound traveled / the distance the solvent travelled.
a high Rf factor of a TLC indicates?
a more NON-POLAR compound since it interacted more with the mobile (non-polar) phase
what is column (flash) chromatography?
the same as TLC but for bulkier compounds.
In column chromatography, the solutions run down the column and are collected in beakers at the bottom. What is the trend of the solutions collected?
the most non-polar are collect first (since they travel fastest with the non-polar mobile phase) and the most polar are collected last
just like TLC, polar travel slowest
what is ion exchange chromatography (explain it as cation exchange)
when saying cation exchange then the stationary phase binds cations.
There is a polymer of anions which is then filled with sodium which bind the anions. Then the solution of mixed charges is run through it. Positive cations will displace the sodium and bind the negative resin (cation exchange) while anions run through the resin quickly. Once all anions are out, the resin is poured with sodium which then displace the desired cations.
in anionic exchange the resin would be positive with some anionic compound interacting such as Cl-.
this is often used for proteins
what is High performance Liquid Chromatography (HPLC)?
what is reverse phase HPLC? (more common)
HPLC is the same as any chromatography but uses pressure to increase rate and efficiency of elution.
reverse phase means the stationary phase is non-polar therefore
POLAR substances run through faster then NON-POLAR ones do.
this is more common than normal HPLC.
what is size exclusion chromatography?
separating molecules based on size often for proteins vs. peptides or different polymers.
the largest molecules elute first
what is affinity chromatography?
Some highly specific molecule binds a protein or nucleic acid of interest from solution. Typically this is an anti-body and antigen interaction.
- add the antibody specific for the protein of interst
- add another molecule that will bind the antigen-antibody complex
- centrifugation separates based on density
- decant and access protein of interest.
using a magnetic beads (2) and a magnet (4) is also possible.
What is gas chromatography?
used for low boiling point (under 100) molecules
there is a mobile gas phase and a stationary liquid phase. Compounds are separated based on how volatile they are. They are heated, they turn to gas and join the inert gas stream into a container
the data of elution is shown on a graph.
what does a high peak indicate in gas chromatography? what does an early peak (relative to time) indicate in gas chromatography?
a high peak indicates there are a lot of gas molecules
an early peak indicates lower boiling point or more volatile.
does branching of a hydrocarbon increase or decrease BP and MP?
decrease since it reduces London dispersion forces.
does intramolecular hydrogen bonding increase or decrease BP and MP
decrease!! since the internal H bonds have less interaction with other molecules
this is why BP of 4 - Nitrophenol > 2-nitrophenol
what are simple and fractional distillations?
boil and re-condense to separate a solution.
fractional is used to separate solutions of close boiling points
what is mass spectroscopy?
used to determine the mass of compounds in a sample. the compound is ionized and then run through a magnetic field.
what is UV spectroscopy?
shoot white light at a compound and observe what colour is reflected / absorbed.
conjugated ring systems absorb the most UV light.
What is IR spectroscopy?
excite bonds with IR to determine functional groups
carbonyl groups - 1700
OH groups - 3200
NMR spectroscopy? What are equivalent hydrogens?
Hydrogens that exist in similar environments reflected through symmetry or rotation.
CH3 - CH2 - OH
3 sets of equivalent hydrogens
if hydrogens are on the opposite side of the molecule but are symmetrical, they are equivalent.
Each set produces a NMR signal
how many sets of equivalent hydrogens on the following?
CH3CH3
CH3CH2CH3
CH3CH2CH2CHO
CH3CH3 - one set of 6 equivalent hydrogens
CH3CH2CH3 - 2 sets of equivalents
CH3-CH2-CH2-CHO - 4 sets
true or false, a proton with n neighbours ( where n = the number of non-equivalent, neighbouring protons) will have n + 1 NMR peaks
true!!
What is NMR splitting?
it explains that for a hydrogen with n non-equivalent hydrogen neighbours, there will be n + 1 peaks for that hydrogen
explain the splitting of
CH3 - CH2 - CH2 - Br
there are three sets of equivalent hydrogens.
hydrogens on the far left have 2 non-equivalent neighbour hydrogens. therefore (n + 1) they have 2 + 1 = 3 peaks on NMR.
in NMR what is a singlet, doublet, etc.
a singlet refers to a hydrogen that produces one peak and therefore has no non-equivalent neighbouring protons (0 + 1)
a doublet produces 2 peaks with 1 nearby non-equivalent H (1 + 1)
etc.
t or f, a molecule may have 3 sets of equivalent hydrogens which all triplets (3 + 3 + 3 peaks) but they are said to only have 3 signals.
true, the amount of equivalent hydrogens explains number of signals. The amount of splitting explains the number of peaks per signal.
