Chapter 29 - Chromatography and spectroscopy Flashcards
what information does thin layer chromatography give?
The number of components in a mixture
what is adsorption?
The process by which the solid holds the different substances in the mixture to its surface
How is separation achieved in TLC?
The relative adsorption of substances within the stationary phase
What needs to be calculated from a TLC plate?
The retention factor
what is the equation for retention factor?
Distance moved by the component divided by distance moved by the solvent front
What is gas chromatography useful for?
Separating and identifying volatile organic compounds
in gas chromatography, what is the stationary phase?
A high boiling liquid absorbed onto an inert solid support
In gas chromatography, what is the mobile phase?
an inert carrier gas
what two pieces of information can be obtained from a gas chromatogram?
The retention times and the peak integrations
what is the chemical test and positive observation for alkenes?
add bromine water drop wise, it will be decolourised from orange to colourless
what is the chemical test and positive observation for Halo alkanes?
Add silver nitrate and ethanol and warm to 50°,
chloro - white precipitate
bromo - cream precipitate
iodo - yellow precipitate
what is the chemical test and positive observation for a carbonyl?
add 2,4-DNP, orange precipitate
what is the chemical test and positive observation for a primary and secondary alcohol and aldehyde?
Add a acidified potassium dichromate and warm, colour change from orange to green
what is the chemical test and positive observation for aldehydes?
Add Tollen’s reagent and warm
, silver mirror
what is the chemical test and positive observation for a carboxylic acid?
Add aqueous sodium carbonate, effervescence
what is resonance?
When the nucleus can absorb energy and rapidly flips between the two spin states
what is measured on an NMR spectroscopy?
The chemical shift
what is used as a standard reference for chemical shift?
TMS
why is it deuterated solvent use?
so the H1 peaks don’t appear
what two pieces of information does C - 13 NMR show?
the number of different carbon environments and the types of carbon environments
what four pieces of information does proton NMR give?
- the number of different proton environments
- the types of proton environments
- the relative numbers of each type of proton
- the number of non-equivalent protons adjacent to a given proton
On an NMR spectra, how do we see the number of different proton environments?
the number of peaks
On an NMR spectra, how do we see the types of proton environment?
chemical shift
On an NMR spectra, how do we see the relative numbers of each type of proton?
integration traces/ ratio numbers of the relative peak areas
On an NMR spectra, how do we see the number of non-equivalent protons adjacent to a given proton?
spin-spin splitting pattern
what rule is needed when analysing the splitting pattern?
n+1
what is different about OH and NH
they can appear at a range of chemical shift values and as broad peaks
how is the problem with OH and NH in NMR spectroscopy overcome?
D2O is added which replaces them and removes the peak
what order should all analytical techniques be done in?
1) Elemental analysis
2) Mass spectra
3) Infrared spectra
4) NMR spectra
