6.3 Analysis Flashcards
what TMS is used for
reference peak for proton NMR spectra
TMS stands for
tetramethylsilane
(CH3)4Si
solvents for proton NMR
sample needs to be in solution
solution must not have any C or H
deuterated solvents used (e.g. CDCl3, D2O)
D2O shake in proton NMR
shake sample with D2O
replaces hydrogen atoms on sample with deuterium
peaks on any functional group containing hydrogen will disappear
chemical shift in proton NMR
protons attached to electronegative atoms will be shifted more downfield (higher PPM)
protons in same environment will have the same chemical shift
spin-spin coupling in proton NMR
high resolution gives more complex signals (doublets, triplets etc)
splitting pattern depends on number of hydrogen atoms on adjacent atoms
splitting pattern formula
number of peaks = number of chemically different H’s on adjacent atoms + 1
ratio of height: draw peaks with heights such as Fibonacci triangle
what integration shows in proton NMR
number of hydrogens at that environment / peak
how coupling occurs
isotopes of the same atom influence each other
why only singlets in carbon NMR
likelihood of C-13 being next to each other in one molecule very rare
solvent definition
liquid used to dissolve things
solute definition
substance that dissolves in a solvent to make a solution
adsorption definition
when particles adhere to the surface of a solid
partition definition
distribution of 2 solutes between 2 phases in a separation process
mobile phase definition
phase which moves through the stationary phase (liquid or gas)
stationary phase definition
phase that doesn’t move
may be a solid (TLC) or liquid (GC) held by solid support
TLC chromatography phases
mobile phase: organic solvent
stationary phase: solid (aluminium oxide or silicon oxide-coated plastic)
thin layer chromatography method
place sample using micro pipette on TLC plate (base line)
place ~1cm^3 depth solvent in beaker
add TLC plate to beaker
add lid to prevent solvent evaporation
leave for mobile phase to reach almost the top
take out TLC and leave to dry (mark where solvent got to)
view results (e.g. with UC, ninhydrin, iodine crystals)
gas chromatography phases
mobile: gas e.g. Ne, Ar, N2
stationary: liquid or solid on a solid support
how gas chromatography works
separation occurs by relative solubility into liquid or adsorption onto solid
retention times measured (longer = less soluble)
limitation of gas chromatography
similar compounds have similar retention times (peaks may hide each other)
hard to identify unknown compounds as retention times depend on flow rate of carrier gas and temperature of column
GC-MS uses irl
analysis in forensics
environmental analysis
airport security
space probes
interpretation of gas chromatogram
peak integrations (area under each peak) can help determine concentration of each component retention times used to identify components by comparing to known components
finding concentration of components method (external calibration)
prepare standard solutions of known concentrations of compound being investigated
obtain gas chromatograms for each standard solution
plot calibration curve of peak area against concentration
obtain gas chromatogram of compound being investigated under same conditions
use calibration curve to measure concentration of compound
nuclear spin for NMR spectroscopy
only detects isotopes with an odd number of nucleons (e.g. 1H or 13C)
region of EM spectrum used for spectroscopy
radio waves
uses of NMR spectroscopy in medicine
MRI scanning
providing diagnostic information
body scanning
melting point determination helps how
determines melting point of substance which:
• helps determine final product (compare to table of known melting points)
• determine purity of product (100% = sharp, range of melting points = not pure)
