spectroscopy and seperation techniques Flashcards
seperation techniques
seperate molecules based on their components
- distillation, chromatography, extraction
analytic techniques
identify compound or determine its properties
spectropscopy
analysis of organic compounds exposed to electromagnetic radiation
bonds appearing in IR spectra
must be polar and have a dipole moment
- OH
what do areas of IR graph show during absorption
valleys, not peaks
fingerprint region
area below 1500 cm-1 on IR graph
where is c=o valley on IR specrta
sharp peak at 1700 cm-1
oh group on IR spectra
broad peak at 3500 cm-1
c=n on IR spectra
1550-1650
c=c on ir spectra
1600-1800
c trip c on ir spectra
2100- 2200
cyanide on ir
2200
nh on ir
3300-3500
what does IR specrta idenfitfy
presence of specific bonds
what does NMR spectroscopy characterize
atoms of a molecule
proton NMR
resonance frequencies
chemical shifts from 0 on right to positive values on left
TMS
reference point on NMR spectra with a peak at 0
upfield shifts
to the right
down field
to the left
what produces an individual peak in proton nmr
each unique hydrogen
area under a peak in proton nmr
represents the number of protons that represent that peak (equivalent)
shift in h NMR depends on
shielding or deshielding of H
if protons are more shielded, what kind of shift do they experience
upfield (right)
if protons are deshielded what kind of shift do they experience
downfield (L)
trend for deshielding
the closer the hydrogens are to an EWG, the more deshielded they will be
aromatic ring shift
about 6.0-8.5
COOH shift
10-11
splitting
n + 1 rule
- peak will split into number of smaller peaks equal to the number of adjacent hydrogen atoms + 1
a carbon with 2 hydrogens and a neighboring carbon with 3 hydrogens would have what kind of peak
a quadruplet
carbon NMR
all peaks are singlets
- equvalent c atoms are a single peak
UV-vis spectroscopy
analyzes absorbance of UV light by organic compounds
- higher frequency than visible light
wavelength of visible light
400 to 700 nm
what kind of molecules tend to absorb UV light
aromatic compounds with conjugated pi systems
- aromatic amino acids
mass spectroscopy
identifying unknown organic compounds by injecting them into a mass spectrometer and high E electrons cause the sample to ionize and become charged
- mass and charge of fragments are plotted on a mass spectrum
x axis - mass to charge ration
y axis is abundance
- largest peak is the base peak which is most abundant fragmemt and gives info about funcitonal group
distillation
seperate liquid from liquid by utilizing differences in the liquids BPs
to ensure purity must do repeated distillations
which liquid will leave the flask first in simple distillation
the one with the lower BP
fractionating column
difference between simple and fractional distillatiom
- not included in somple
simple distillation
seperation of two liquids with very different boiling points
- at least 25 C apart
simple distillation
seperation of two liquids with very different boiling points
- at least 25 C apart
- no fractioning column
fractional distillation
seperate liquids with similar bps (less than 25 C)
vaccum distillation
- when bp reach 400 c, cannot raise the tempretaure, must decrease the atmospheric pressure to meet vapor p
boiling pt
temperature at which vapor pressure is equal to atosopheric pressure
liquid- liquid extraction
seperate liquids based on solubitility in organic or aqueous media using a seperatory funnel
- require 2 immiscible liquids
- should be conducted several times to purify
chromatography
seperation technique with a mobile phase and a stationary phase
Thin Layer chromatography
stationary phase : polar
mobile phase : non polar
- nonpolar molecules move farther and have a larger RF
do polar molecules in TLC have a high or low RF
retention factor low because doesn’t move
retention factor RF
distance traveled by the molecule compared to the total distance the solvent travels
0< RF < 1
- RF closer to 1 means non polar
RF closer to 0 means polar
column chromatography
isolates and purifies
stationary phase: solid
mobile phase liquid
size exclusion chromotography
omit larger molecules first, smaller molecules remain in the column
stationary phase: gel beads that trap small molecules
cation exchange chromotography
want to keep cations in the column, anions are eluted
- anions are lined within the column to attract cations `
anion exchange chromotography
want anions to remain in the stationary colimn
- cations eluted
- cations line the column
affinity chromotography
seperate molecules based on ligands and affinity for them
stationary column lined with ligands and keep molecules that bind, elute the ones that dont q
gas liquid chromotography
only technique that involves a gas mobile stage
stationary phase coated in liquid
- time taken to move through denotes affinity for gases and liquids - longer time to elute = stronger affinity for liquid
- quicker time to elute = stronger gas affinity
high performance liquid chromotography
liquid mobile phase and absorbant column
- differentiation: high pressure so resolution is more rapid
- stationary phase: polar
- mobile phase: liquid nonpolar
requirement for gas chromotography
need a substance that can easily be forced into gas phase , one that does not vaporize below 700C is a bad choice
reverse phase - high performance liquid chromotography
reverse phases of HPLC and TLC
mobile phase: polar
stationary: nonpolar
recrystallization
solid percipitates out of solution and do over several times to purify
- in solvent that crystal is highly siluble in at high temp
- insolible at low temp
