organic compound analysis Flashcards
m/z
mass-to-charge ratio
mass spectromery uses
calculate molecular weights of sample’s contents
identify unknown compounds and their physical structure
distinguish between isomers
stages in mass spectronmeter (instrument)
1) sample is vaporised
2) ionisation: bombarded w electrons -> framgents
3) deflection by magnetic field
4) detection
only positively chared particles are measured and compound must be (g)
how are compounds ionised in mass spectrometry (show an equation)
bombardment with electrons knock of an electron
eg X+ e- -> [X]+ + 2e-
(need to be able to show ionisation equation)
fragmentation
breaking of almost any bond in a molecular ion into a fragment and an alkyl group
eg M+ -> X+ (FRAGMENT) + R.
dot in R. represents unpaired electron. R. is not +vely charged
base peak
molecular ion peak
base= most abundent fragment
molecular/parent= highest Mr
IR spectroscopy function and principles
principle= use infrared radiation to vibrate covalent bonds making the bonds bend/stretch
function= info about covalent bonds, functional groups and structure/ type of molecule
possible uses of IR spec
- identify org compounds
- design new drug
- analyse proteins
- testing blood alcohol
relationship between bond strength and the absorption of IR radiaion
weaker bonds require a lower fq of radiation to vibrate bonds
bond that vibrates a higher fq adsorbs IR radiation with a higher wave#
relationship between mass and IR absorption
atoms with higher masses absorb lower frequency radiaion
how to tell IR with most amount of C-H bonds/ longest chain
more peaks in fingerprint region
NMR
Nuclear Magnetic Resonance spectroscopy => determine entire structure/ provides structural information
magnetic field interacts with nuclear spin of atoms
- short powerful radio pulse absorbed by nuclei -> flip to high nrg spin status
- spectrum produced when nuclei return to low nrg spin states releasing a pulse of nrg
fts of NMR
form of absorbance specroscopy
v fast
v expensive and hazardous bc of strong magnetic field
qualitative data
chemical shift
distance from standard peak (far right given by standard compound TMS= tetra methyl saline which has lowest known chemical shift=0)
why is the chemical shift different for different hydrogen environments
Because diffent hydrogen environments have different atoms surrounding its nucleus, this affects the amount of chemical shielding experienced thefore affecting the energy emitted from the nucleus spinning
area under peak
ratio of hydrogens in environment
splitting patern
number of hydrogens on neighbouring carbons (only H NMR)
number of peaks=
number of neighbouring H atoms (n) + 1
1 neighbouring = doublet ect
chromarography
technique to separate substances in a mixture
- stationary phase
- mobile phase
Sample _ _ to the stationary phase
and _ _ to the mobile phase
adsorbs and desorbs
which molecules are more attracted to the polar stationary phase
polar molecules
stationary phase
solid onto which compounds of a sample adsorb
mobile phase
phase that flows through stationary phase carrying components of a sample with it
adsoption
desorpion
ad= components adhere to the stationary phase
de= component released from the stationary phase and dissolves into mobile phase
what effects the rate substances move along the stationary phase
solubility in mobile phase (higher solubility -> shorter reention time)
strength of adsorption to stationary phase (stronger -> longer retention time)
which moleculesa are more attracted to polar solvents
polar molecules
how to determine which sample has most strongly adsorbed to the stationary phase
the sample which has moved the least amount of distance through the column due to strong attraction to the stationary phase
how to determine the component which is least atracted to the stationary phase
q
the component that has moved the greatest distance through the column. That component would have adsorbed ino the stationary pahse and desorbed back into the mobile rate at a faster rate than the other components in the system
explain separation of two different components in chromatography
-> separation occurs as components move with different rates of adsorpion to the stationaruy phase and desorption to the moile phase
-> one component move least distance bc more strongly adsorbs to stationary phase
-> other component moves most distance bc less strongly adsorb to stationary phase and more readily desorbs to mobile phase
retention time
amount of time a sample stays in the COLUMN
longer rt if sample
- adsorbs more strongly to stationary phase
- are bigger tf carried more slowly by mobile phase
position of peaks in HPLC chromotograms
represent RT
area under chromatogram peak
link to concentration of component in sample, greater amount of component, greater AREA under peak
fatcors affecting rt
length of ccolumn
temperature
surface area of stationary phase
identity/composition of stationary and mobile phase
stardard solution
solution with accurately known concenration
HPLC
high performance liquid chromatography
measure large compounds
stationary phase= fine particle waxy solids
mobile phase= pure solvent pumped under high pressure that helps move substance thru densly packed column
measures rt
q
interpolation
values exist within range of measurements
reliable
primary standards
used to make standard solution:
- pure form
- known chemical formula
- easy to store without deterioating/reacting w atmosphere
- high Mr
- inexpensive
eg anhydrous Na2CO3
equivalence point
neither reactant is in excess and reactants have reacted in exact molar ratio
why is it at equivalence point, pH is not always 7
due to acid-base properties of conjugate products that might be formed
what can affect the titre required to achieve the endpoint
(for ans, assuming acid in conicle flask and base in burette)
dilution of base in burette (change in conc of base)
change in type of acid ie monoprotic vs diprotic (change in conc of H ions)
NOT DILUTION OF ACID OR USE OF WEAKER/STRONGER ACID
finding mol of compound in vol flask from aliquot
[mol of aliquot] divided by [ml of aliquot] multiplied by [ml of flask]
rf value calc
distance travelled from origin / distance travelled by solvent front from origin
products of esterification reactions
WATER and ester
extrapolation
values outside range of data tf predictions are unreliable
how to explain whether selction of indicator is appropriate (structure)
- state equivalence point (below/above/at 7)
- “a pH indicator that has a pH range similar below/above/at 7 is appropriate)
- state indicator range and whether it is inside/outside steepest section of pH curve tf not/appropriate
- suggest beter indicator if not
standard soln
solution w an accurately known concentration
%w/w
g per 100g of mixture
%w/v
g per 100mL of soln
%v/v
mL per 100mL of soln
%v/v
mL per 100mL of soln
ppm
microgram per gram of mixture
ppb
g in a billion grams
