Sum of Double bonds And Rings -- unsaturation index
(2n+2) - Hs - Xs + Ns, ignore Os, / 2
DON'T FORGET TO DIVIDE BY 2
purpose of melting point
identification and purity. If Mpt is low, compound is impure.
do it twice--once to get a broad range, once to get the actual range.
Always a range.
How to load a capillary tube
tap a little in, turn it right side up and drop it down the giant tube--let gravity load it.
purpose of boiling point
Impurities make the boiling point higher--opposite of melting point.
Dependant on pressure. Higher pressure makes a higher boiling point.
IR fingerprint region
1000-1600 or so
four types of distillation
simple (separate any liquid from any solid)
steam (natural products in small amounts, using water)
vacuum (compounds that decompose at their boiling points--reduce the pressure to decrease the boiling point)
fractional (2 boiling points are very close. Long, fat column)
Why soak and grind in oil/steam distillation
soak to rehydrate and grind to increase surface area
thing that you put into a solution to prevent bumping and frothing
Where does the thermometer go in distillation and why
has to be very close to but not in the liquid. Too high and you will simply record the steam temperature, which is always the same
in extraction. K = [Solubility in solvent 1] / [solubility in solvent 2]
the higher the partition coefficient, the more moves from one to the other with each extraction.
How does extraction work?
Take a nonpolar substance and get it in a polar solvent, mix in methylene chloride (or other nonpolar) in a separatory funnel. Mix, vent, mix, vent, take out the chloride.
Boiled tea with sodium carbonate. Tannic acid is soluble in sodium carbonate and caffeine isn't (because it's a base). Caffeine is soluble in methylene chloride
Multiple times to get more pure--higher partition coefficient gets you more pure each time. Only need 1 extraction if K = 5 or more. Ideal.
Removing acid from an acid-base compound
mix in a base and the acid will come out
Why a tiny spot in TLC
so it's won't spread out. Need to keep resolution and stop spots from merging.
When do you add methylene to hot tea?
Let it cool ! Methylene chloride has a very low boiling point and will explode and evaporate if poured into a liquid that's over 40 degrees.
How did we see the spots in TLC?
UV light. Plate included a fluorescent, so dark spots were the compound.
If no UV, an iodine chamber can be used. Jar with iodine crystals.
Distance traveled by substance / distance traveled by solvent front
"retardation factor". Can't really be duplicated--need both on the same plate to compare.
Best solvent for crystallization
a sharper temperature gradient, therefore a more vertical line. You want something that will have extremely different solubilities at different temperatures.
point of crystallization
to purify/separate compounds.
provides a small nucleus and surface area to start crystallization. Adding a piece of pure aspirin would also do it.
Mobile and stationary phase
TLC. The plate is the stationary phase, the liquid is the mobile phase.
Moves by capillary action
a too-mixed compound. Can't be extracted because it can't be separated.
Salicylic acid (benzene ring with COOH and OH attached) + acetic anhydride (CH3 C=0,0,C=0 CH3) <---H+----> Acetylsalicylic acid (benzene ring with COOH and COO CH3 attached) + acetic acid (CH3COOH)
Acid catalyst (sulfuric)
Limiting reagent and theoretical yield
Change everything to moles. Whichever element has the least moles is the limiting reagent. However many the least moles is is how much product you could theoretically get. Convert back to grams or whatever.
SODAR of aspirin
2x9-2 -8 /2 = 4
Act of aspirin synthesis
salicylic acid, acetic anhydride and acid (sulfuric) catalyst
add water to break down anhydride to acetic acid. Aspirin is insoluble in water. Separates from acetic acid.
Compounds in the aspirin solution at the end
Sulfuric acid, aspirin, acetic acid and salicylic acid.
Why dry TLC plate
to remove the moisture in the air from the plate to get a really good reading.
What's on a TLC plate?
silica gel and fluorescent
How do TLC plates work?
Solvent must decide if it's more soluble in liquid or sand (higher or lower Rf). The more polar, the higher Rf. Silica is polar. Most compounds are nonpolar
What do you do if you THINK you have pure benzoic acid?
Get the melting point, then mix it with pure benzoic acid. If the melting point stays the same, then it is. If not, it will drop with impurities
How does the IR machine work?
Infrared radiation (small wavelengths, high frequency = more energy).
Put the compound between two blocks of salt.
IR indicates the vibration of molecules excited by the wavelength.
Degrees of freedom
3n-5 for a linear molecule
3n-6 for a nonlinear molecule
n is number of atoms. 3 comes from the three axes. There is also rotation.
ex. HCN is linear, 3(3)-5=4 degrees of freedom.
Higher numbers make more peaks
What are the funnels and what are they for?
Buchner and Hirsch, for filtration
Any natural compound will be a...
mixture. Not pure.
What is activated charcoal for?
removing impurities, particularly colored impurities, by absorption