Chapter 20 Chromo Flashcards
How does TLC work
Two phases, stationary and mobile phase. The stationary phase is the adsorbent normally, which is thr silica powder. Here the adsorbent is the thing that absorbs other stuff.
Based on the varying degree of interaction strentgh the substance has with the mobile phase compared to the adsorbent silica powder will determine how far the thing travels. If more attracted to stationary wint travel far at all, if it is then it will travel further .
This is how separation is achieved.
How to e ir fly di one
Pencil line 1 cm from bottom, spot on top and keep adding it and drying using capillary tube
Make sure on line, add less solvent in a beaker so it doesn’t dissolve, then put watching glass on top to prevent evaporation of the solvent,
Let it travel up, once up take out and write the pencil line
Finally need to reveal the spots .
How to reveal the spots
1: use UV lamp and then try circle
2) spray with idodine crystals let them sublime
Or other chemical to make it show
Finally use retention factor value which is ratio of how far solvent moved compared to thing and based on specific solvent csn compare in a data base.
- alternatively run the compound against KNWON SAMPLES OF PURE SUBSTANCE.
That way yiu can just MATCH THEM UP TO FIND OUT
How does gas chormatgrluphy work
Used to identify and separate VOLATILE organic mixtures this time
Here the stationary phase is inside the column, actually a liquid adsorbed onto an inert solid
Mobile phase inert gas like helium
The gas sample is injected and vaporised and carried by the mobile phase through coloumn. If more soluble with liquid stationary phase, then that gas will take longer to escape the chromagraph apparatus.
These specific times are known in data base, and that’s how you can tell
How to interpret gas chromatgrom
What two things can you see and how to use
The retention time shows you differnt sources
The peak integration area represents relative concentrations, so more means more concentration if that
To find out, once you identified what the thing is, prepare known concs of it, reun it in chromatgrom, record different areas, plot s calibration curve, and dismally use it to exert image
Test for haloalkane proeperly
Silver nitrate obviously and this produced orecispted milk cream butter! Which then dissolve in varying degrees of ammonia
Here must use aqeuousnsilve nitrate and ethanol, and heat to 50° in a water bath
How does NMR work
Based on the NUECLEONS of an atom to absorb this time radio wave and cause them resonate
This is because nucleons have a property called NUCLEAR SPIN, like electrons had. Nuc,ear spin can FLIP BETWEEN ITS STATES with the right amount of energy provided to them, and this flipping is called RESONANCE .
However this can only take place if there are AN ODD NUMBER OF NUCLEONS.
Energy given in, different ranges of radio wave, and based on what comes out you can tell what went in, and based on what went in usign chart determine functional groups
Why is it so useful for identification
This is because we said can only be used for ODD number of nucleons , and everything pretty much has a CARBIN 13 isotope in a few hundred molecules
And hydrogen is odd too
And the fact is yiu dint have to use TRADIAONAL CHEMICAL TEDTS AND DETSRIYBTHE SAMPLE ETC
How is different energies needed
This is because with different number of electrons surrounding thr nfukeud with differnt atoms, will means different energy is needed for nuclear resonance to take place
Thus with a different atom, the energy required SHIFTS, known as a helical shift which is measured agsisnt a standard TMS which has a shift of 0
So based on what the atoms are boned to , the different enevruonemnts creates shifts
Why even no?
Not even because this will always allign itself in the MAGENTIC field
Why is TMS used 3 reasons
Last reason, does it produce any frequencies of it’d own?
Always will be a small shift caused by TMS at 0
TMS is used for
- inert so won’t react
- easily volatile so can be taken out
- ITS A SYMMETRICAL MOLECULE, meaning there is exactly 1 carbon environment and 1 proton environment, meaning it only produces 1 frequency, making it a goof thing to COMPARE TOO
How is a sample prepared for NMR
1) dissolved in a solvent and placed in a tube
2) TMS added
3) spun around ti even imperfections in MAGENTIC field
4) zeroed against TMS and radio waves are pulsed through
Based on what comes out can tell what was absorbed
What are deuteurated solvents and why used
These are solvents that use 2H instead of normal hydrogen. As this has EVEN NUMBER OF NUCLEONS, it means NO PEAK WILL BE PRODUCED FOR THE SPEC. As a result, they’re hseuful to use for solvents which is needed to rorowre a sample
Or if it dies produce a peak, it will be filtered out by the computer pretty quickly first
So USED AS SOLVENTS AS PRODUCE NI PEAK
Explain peaks , number of them, and why they different
Every time there is a CARBON ENVIRONMENT, there is a peak, so number of peaks = environments
A carbkn envriomemt identified by looking at atoms around it. Different atoms = different environment, BUT ALSO PRODIMITY TO THE ELECTRONEGATIVE ATOMS DETERMINES DIFFERENT CHEMICAL SHIFTS TOO
don’t forget that IF SYMMETRICAL, they exist in same environment, so will contribute ti the same peak, so not another peak
And remember symmetrical can go wacky three ways aswell, watch out
Why can their be two peaks in same range of thr soec
This is because they are different environments because one is more close to the electronegative atom than the other
And also the closer you are to an electronegative atom, thr MORE SHIFTED TOU WILL BE
