Spectroscopy and Chromatography Flashcards
What does the mass spectrometer detect?
The mass to charge ratio of the molecular ion, which gives the molecular mass of the compound.
How are molecular ions formed in mass spectrometry?
Electron is lost to form a positive ion
How is molecular mass found from a mass spectrum?
The molecular ion peak (M+ peak) has to be located.
What is the cause of the M + 1 peak?
Some carbon is present as the carbon-13 isotope.
What is fragmentation?
The molecular ions break down into smaller pieces called fragments.
What causes the other peaks in a mass spectrum?
Fragment ions
How can a mass spectrum differentiate between structural isomers?
They will break apart differently and thus will have different mass spectra.
What is the effect on a bond when it absorbs IR?
Bend or stretch more as they gain energy.
What does the amount a bond streches or bends depend on?
Mass of the atoms in the bond - heavier atoms vibrate more slowly than lighter atoms
Bond strength - Stronger bonds vibrate faster than weaker bonds
What is unique about each bond with regards to IR absorption?
Can only absorb radiation that has the same frequency as the natural frequency of the bond.
What scale is used for the frequency values on ir spectroscopy?
Wavenumber 200/cm to 4000/cm
How does infrared spectroscopy work?
Sample placed inside an IR spectrometer,
A beam of IR radiation in range 200/cm to 4000/cm passed through the sample
Molecule absorbs some of the IR frequencies and the emerging beam is analysed to find the absorbed frequencies.
What is the term given to the dips in the graph?
Peaks
What do peaks help us predict?
The bond types in the molecules.
What is below 1500/cm known as on the IR spectrum and why?
Fingerprint region
The peaks in this region are unique to each molecule.
In an exam question what can be used to determine the molecule in question?
IR absorptions on formula sheet
What is the typical sequence for identification of an unknown substance?
Elemental analysis - determine empirical formula
Mass spectrometry - Determine molecular mass and identify sections in molecule from fragment ions
Infrared spectroscopy - identify bonds and functional groups present
Identity of unknown compound can be worked out now.
What are the two phases for all forms of chromatography?
Stationary phase
Mobile phase
What is the stationary phase?
Does not movewhere a solid or a liquid supported on a solid
What is the mobile phase?
Does move its Normally a liquid or a gas
What is a TLC plate made of?
a TLC plate is made of a Plastic/glass sheet Coated with thin layer of a solid adsorbent substance such as silica
Outline adsorption in reference to TLC
Process by which the solid silica holds the different substances in the mixture to its surface
How is the retention factor calculated?
Rf= Distance moved by the component/distance moved by the solvent front
What is gas chromatography useful for?
Separating and identifying volatile organic compounds present in a mixture
What are the different phases for gas chromatography?
1) Stationary - high boiling liquid adsorbed onto an inert solid support
2) Mobile - is an inert carrier gas such as helium
How does time taken to move through the column change as solubility in stationary phase increases?
The more soluble the component is in the liquid stationary phase, the slower it moves through the capillary column.
What is retention time?
Time taken for a component to travel through the column
How is retention time used for identification?
Compare to retention times in database
What can peak integrations for gas chromatograph be used to determine?
Concentrations of components in the sample
what’s the test for carboxylic acid?
Add aqueous sodium carbonate, positive = effervescence
what’s the test for a primary and secondary alcohol and aldehyde?
add acidified potassium dichromate (VI) and warm in a water bath. Positive is a colour change of orange to green
what’s the test for a carbonyl?
Add Brady’s Reagent, orange ppt is positive for C=O group
what’s the test for a haloalkane?
Add silver nitrate and ethanol and warm in 50 degree water bath:
White ppt - Chloroalkane
Cream ppt - Bromoalkane
Yellow ppt - Iodoalkane
what’s the test for an Alkene?
decolourises bromine water from orange to colourless
What is resonance for NMR?
When the nucleus absorbs energy and rapidly flips between the two spin states
what must the nucleus of an atom have to work with NMR?
it must have an ODD number of nucleons to work.
What is the standard reference chemical for NMR?
Tetramethylsilane (TMS)
(CH3)4Si
What is the purpose of D2O as a solvent in proton NMR spectroscopy?
O-H peaks no longer appear
what two pieces of information does analysis of carbon-13 NMR show?
The two pieces of information analysis of carbon-13 NMR shows is:
1) The number of different carbon environments from the number of carbon peaks
2) the types of carbon environments present from the chemical shift
what would the proponal carbon nmr spec look like?
3 Peaks
example of propanone, what would the carbon nmr spec look like?
2 peaks
what four pieces of info does the proton nmr spec tell you?
the proton nmr tells you 4 pieces of info:
1) number of proton environments
2) Types of proton environments
3) the relative numbers of protons
4) The number of non-equivalent protons adjacent to a given proton
what are the names of the different H NMR peaks?
Singlet - No H on adjacent atoms
Doublet - Adjacent CH
Triplet - Adjacent CH2
Quartet - Adjacent CH3
Multiplet - Adjacent to C with more than 3 H
what are some common splitting patterns?
Quartet next to Triplet = CH2-CH3
Triplet - Doublet = CH-CH2
Triplet - Triplet = CH2-CH2
Doublet - Doublet = CH-CH
Quartet - Doublet = CH-CH3
Multiplet (7 Peaks) - Doublet = CH-(CH3)2
how does gas chromatography work?
1) Stationary - high boiling liquid adsorbed onto an inert solid support
2) Mobile - is an inert carrier gas such as helium
3) small amount of volatile mixture is injected into the gas chromatograph
4) The mobile carrier gas carries the component in the sample through the capillary column containing the stationary phase
5) the more soluble the component is in the liquid stationary phase, the slower it moves through the capillary column
