Class Two Flashcards
what does solubility depend on
polarity of the solute and the polarity of the solvent
polar molecules are soluble in..
polar solvents
how to extract organic amines
with acidic water solution
protonates the basic functional group (forms a positively charged ion) → cationic salt
how to extract carboxylic acids
extraction with a dilute weak base → anionic salt
how to extract phenols
sodium hydroxide → converts phenols into their anionic salts
what does a separatory funnel allow for
allows for you to extract a specific substance by separating the other ones
uses of chromatography
identification purposes
purification
thin layer chromatography
compounds are separated based on differing polarities
how does TLC work
a mobile liquid phases ascends a thin layer of absorbent that is coated onto a supporting material (glass plate)
purpose of absorbant in TLC
acts as a polar stationary phase for the sample to interact with
why does separation occur in TLC
because different compounds travel along the plate at different rates
polar components interact with absorbant → travels slower
Rf value - TLC
the distance traveled by an individual component divided by the distance travelled by the solvent front
column (flash) chromatography
similar concept to TLC → used for bulk compounds
ion exchange chromatography
separates materials with varying charge states
when is ion exchange chromatography frequently used
separation of protein mixtures
(proteins within a mixture exist in a variety of charge states)
pI vs pH matters as well (pI > pH is positively charged)
high performance liquid chromatography
speed and efficiency of separation is increased (higher pressures mobile → stationary)
size exclusion chromatography
used to separate bulk materials based on molecular size
uses polymer beads with pores - allows for small molecules to go through, but not large ones
large ones go through a different (faster) pathway
affinity chromatography
used to purify proteins or nucleic acids from biochemical mixtures
target molecule gets trapped on the stationary phase
different ways of using affinity chromatography
protein linked beads (target protein binds)
magnetic beads (target protein binds)
what is an affinity tag
molecular tags that act as an antibody (binds to target protein)
gas chromatography
separation of mixtures based on their different volatilities
less volatile components spend more time dissolved in the liquid stationary phase
the more volatile components leave the column first
branching (melting & boiling points)
branching reduces attractive forces (van Der Waals) between molecules → lower melting and boiling points
molecular weight (melting & boiling points)
the greater the molecular weight → more SA → more areas for van Der Waals interactions → higher MP and BP
small hydrocarbons tend to be ___ at room temp.
gases
intermediate hydrocarbons tend to be ___ at room temp.
liquids
large hydrocarbons tend to be ___ at room temp.
solids
hydrogen bonding ___ MP and BP
increases
which has a higher effect on MP and BPs? intra or inter H bonding
intermolecular hydrogen bonding
what is distillation
raising the temp of a liquid → vapour → condensed back into the liquid phase in another container
when is a simple distillation performed
when trace impurities need to be removed from a relatively pure compound
what is fractional distillation
used when the difference in BPs of the mixture components is not large
top of the column = pure vapour (condensed + collected in its liquid phase)
what is mass spectrometry
technique that can determine the mass of compounds in a sample
what is UV spectroscopy used for
transition metals (promotions of their electrons)
conjugated organic systems
IR spectroscopy
range of 2.5-20 um (causes bonds in organic molecules to become vibrationally excited)
the higher the wavenumber..
the higher the frequency and greater the energy
C=O stretch
1700 cm-1
very strong & intense
if the C=O stretch is not present..
you can eliminate compounds that contain a carbonyl group
e.g. aldehydes, ketones, carboxylic acids, esters, amides, anhydrides etc.
C=C stretch
1650 cm-1
triple bond stretch
C to C
or
C to N
2260-2100 cm-1
O-H stretch
strong and broad
3600-3200 cm-1
why is the O-H stretch broad
due to H bonding
C-H stretch
3300-2850 cm-1
aliphatic C-H bonds wavenumber
less than 3000 cm-1
NMR spectroscopy
light from the radio frequency range of the electromagnetic spectrum is used to induce energy absorptions
equivalent hydrogens have..
identical electronic environments - identical locations in the NMR spectrum
when are hydrogens considered equivalent
when they can be interchanged by a free rotation or symmetry operation
when does spin spin splitting occur
when nonequivalent hydrogens interact with eachother
degree of splitting
n + 1
where n = number of nonequivalent neighbouring protons
what is an integration - NMR
measurement of the area under each absorption peak (resonance) → indicatives the number of protons for each peak
what is a chemical shift - NMR
indicates the location of resonance (peaks) in the NMR spectrum
less deshielded protons will appear..
upfield (right)
more deshielded protons will appear..
downfield (left)
factors involved in proton deshielding
the electronegativity of the neighbouring atoms
hybridization
acidity and hydrogen bonding
if an electronegative atom is close to a proton.. (chemical shift)
it decrease the electron density near the iron → deshielding therefore downfield shift
what is the hybridization effect
a result of the varying bond characteristics of carbon atoms connected to hydrogens
the greater the s-orbital character of a C-H bond.. (chemical shift)
the less electron density on the H → more deshielded so downfield shift
protons attached to heteroatoms are..
very deshielded
heteroatoms = O or N
extreme example of a very large downfield shift
acidic protons on a carboxylic acid
fractional distillation is useful for separating..
diastereomers
how to resolve enantiomers
convert the enantiomers to diasteromeric salts with a chiral resolving agent (acid)
separate the salts
revert the salts back to the original compounds
length of chain of sp2 hybridized atoms & UV
as the chain increases, the wavelength of light absorbed increases (redshifts)
the colour we see..
is the complementary colour of the wavelength that is absorbed
