PRELIM 1 Flashcards
why do impurities lower melting point
they increase disorder in a lattice structure (increase ∆S which decreases T melting)
why do impurities broaden melting point range
earlier detection of melting point, impurities have different melting points
list purity techniques
TLC (count # spots), melting point (assess range), recrystallization (remove impurities at different temperatures), extraction (remove unwanted layers)
list separation techniques
TLC, column chromatography, extraction, heating
list identification techniques
melting point, IR, TLC (comparisons to standard)
stationary phase
silica, polar because hydrogen bonding
what compounds can bind to stationary phase (and have what element)
polar compounds, extra H’s
mobile phase
less polar, moving via capillary action
iodine vapors dip
makes brown spots
olefin dip (potassium permanganate)
makes yellow/brown against purple
when to use olefin dip
oxidizable (remove H from carbon) alcohol, aldehyde, alkene, alkyne
phosphomolybdic acid dip
universal green/brown spots
p-anisaldehyde
various colors against pink
when to use p-anisaldehyde
nucleophiles, oxygenated compounds (have an O)
what does increasing polarity of solvent do to Rf
increases RF
define partition coefficient
ratio of concentrations of compounds in mixture of 2 immiscible solvents at equilibrium
increasing Kc of octanol to water = ?
increase across blood-brain barrier
Lipinskin’s rule of 5
likelihood drug is orally bioavailable
extraction
compound of interest moves layers
washing
compound of interest stays in layer
increasing steps of extraction =
increased mass of compounds in organic layer and increased surface area
recrystallization relies on..
Ksp and differential solubilities of contaminants and target compounds AND/OR different amounts of impurities and compound
when does recrystallization work best
if starting material is relatively pure
solvent of recrystallization
high temperature coefficient
at high temp: dissolve most compound, impurities insoluble
at low: dissolve little compound (is crystals), impurities soluble
why cool slowly in recrystallization
if fast, it traps impurities in the crystals by fast precipitation
why no evaporating on hot plate
can set organic vapors that are denser than air on fire
what does heating mantle do
heats; no thermostat
what does voltage regulator do
control heat
why heating mantle elevated using wood
need to remove heat easily by lowering it
water in is at the ___ and water out is at the ___ (reflux)
bottom, top
steam is in at the ___ and water is out at the ___
top, bottom (if not, flood)
eutectic point
ratio of compounds in a mixture that elicits the lowest melting point for that mixture
is H2O or OH- a better leaving group
H2O because weaker base; accepts electrons better
oxidation
increasing bonds to oxygen; decreasing bonds to hydrogen
reduction
decreasing bonds to oxygen; increasing bonds to hydrogen
